PEP 3114: rename .next() to .__next__() and add next() builtin.

Doc/api/newtypes.tex

@@ -1071,7 +1071,7 @@ The next two fields only exist if the
   iterator, or raises \exception{StopIteration} when the iterator is
   exhausted.  Its presence normally signals that the instances of this
   type are iterators (although classic instances always have this
-  function, even if they don't define a \method{next()} method).
+  function, even if they don't define a \method{__next__()} method).
 
   Iterator types should also define the \member{tp_iter} function, and
   that function should return the iterator instance itself (not a new

Doc/howto/functional.rst

@@ -199,11 +199,13 @@ foundation for writing functional-style programs: iterators.
 
 An iterator is an object representing a stream of data; this object
 returns the data one element at a time.  A Python iterator must
-support a method called ``next()`` that takes no arguments and always
+support a method called ``__next__()`` that takes no arguments and always
 returns the next element of the stream.  If there are no more elements
-in the stream, ``next()`` must raise the ``StopIteration`` exception.
+in the stream, ``__next__()`` must raise the ``StopIteration`` exception.
 Iterators don't have to be finite, though; it's perfectly reasonable
 to write an iterator that produces an infinite stream of data.
+The built-in ``next()`` function is normally used to call the iterator's
+``__next__()`` method.
 
 The built-in ``iter()`` function takes an arbitrary object and tries
 to return an iterator that will return the object's contents or
@@ -218,13 +220,13 @@ You can experiment with the iteration interface manually::
     >>> it = iter(L)
     >>> print it
     <iterator object at 0x8116870>
-    >>> it.next()
+    >>> next(it)
     1
-    >>> it.next()
+    >>> next(it)
     2
-    >>> it.next()
+    >>> next(it)
     3
-    >>> it.next()
+    >>> next(it)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
@@ -271,7 +273,7 @@ won't return either.
 Note that you can only go forward in an iterator; there's no way to
 get the previous element, reset the iterator, or make a copy of it.
 Iterator objects can optionally provide these additional capabilities,
-but the iterator protocol only specifies the ``next()`` method.
+but the iterator protocol only specifies the ``__next__()`` method.
 Functions may therefore consume all of the iterator's output, and if
 you need to do something different with the same stream, you'll have
 to create a new iterator.
@@ -485,7 +487,7 @@ outputs the value of ``i``, similar to a ``return``
 statement.  The big difference between ``yield`` and a
 ``return`` statement is that on reaching a ``yield`` the
 generator's state of execution is suspended and local variables are
-preserved.  On the next call to the generator's ``.next()`` method,
+preserved.  On the next call ``next(generator)``,
 the function will resume executing.  
 
 Here's a sample usage of the ``generate_ints()`` generator::
@@ -493,13 +495,13 @@ Here's a sample usage of the ``generate_ints()`` generator::
     >>> gen = generate_ints(3)
     >>> gen
     <generator object at 0x8117f90>
-    >>> gen.next()
+    >>> next(gen)
     0
-    >>> gen.next()
+    >>> next(gen)
     1
-    >>> gen.next()
+    >>> next(gen)
     2
-    >>> gen.next()
+    >>> next(gen)
     Traceback (most recent call last):
       File "stdin", line 1, in ?
       File "stdin", line 2, in generate_ints
@@ -521,7 +523,7 @@ You could achieve the effect of generators manually by writing your
 own class and storing all the local variables of the generator as
 instance variables.  For example, returning a list of integers could
 be done by setting ``self.count`` to 0, and having the
-``next()`` method increment ``self.count`` and return it.
+``__next__()`` method increment ``self.count`` and return it.
 However, for a moderately complicated generator, writing a
 corresponding class can be much messier.
 
@@ -583,7 +585,7 @@ use parentheses when there's an operation, as in ``val = (yield i)
 Values are sent into a generator by calling its
 ``send(value)`` method.  This method resumes the 
 generator's code and the ``yield`` expression returns the specified
-value.  If the regular ``next()`` method is called, the
+value.  If the regular ``__next__()`` method is called, the
 ``yield`` returns ``None``.
 
 Here's a simple counter that increments by 1 and allows changing the
@@ -604,18 +606,18 @@ value of the internal counter.
 And here's an example of changing the counter:
 
     >>> it = counter(10)
-    >>> print it.next()
+    >>> print next(it)
     0
-    >>> print it.next()
+    >>> print next(it)
     1
     >>> print it.send(8)
     8
-    >>> print it.next()
+    >>> print next(it)
     9
-    >>> print it.next()
+    >>> print next(it)
     Traceback (most recent call last):
       File ``t.py'', line 15, in ?
-        print it.next()
+        print next(it)
     StopIteration
 
 Because ``yield`` will often be returning ``None``, you

Doc/lib/libcollections.tex

@@ -174,7 +174,7 @@ def roundrobin(*iterables):
     while pending:
         task = pending.popleft()
         try:
-            yield task.next()
+            yield next(task)
         except StopIteration:
             continue
         pending.append(task)
@@ -315,12 +315,12 @@ letter.
 
 The function \function{int()} which always returns zero is just a special
 case of constant functions.  A faster and more flexible way to create
-constant functions is to use \function{itertools.repeat()} which can supply
+constant functions is to use a lambda function which can supply
 any constant value (not just zero):
 
 \begin{verbatim}
 >>> def constant_factory(value):
-...     return itertools.repeat(value).next
+...     return lambda: value
 >>> d = defaultdict(constant_factory('<missing>'))
 >>> d.update(name='John', action='ran')
 >>> '%(name)s %(action)s to %(object)s' % d

Doc/lib/libcsv.tex

@@ -487,8 +487,8 @@ class UTF8Recoder:
     def __iter__(self):
         return self
 
-    def next(self):
-        return self.reader.next().encode("utf-8")
+    def __next__(self):
+        return next(self.reader).encode("utf-8")
 
 class UnicodeReader:
     """
@@ -500,8 +500,8 @@ class UnicodeReader:
         f = UTF8Recoder(f, encoding)
         self.reader = csv.reader(f, dialect=dialect, **kwds)
 
-    def next(self):
-        row = self.reader.next()
+    def __next__(self):
+        row = next(self.reader)
         return [unicode(s, "utf-8") for s in row]
 
     def __iter__(self):

Doc/lib/libdis.tex

@@ -529,10 +529,10 @@ Set byte code counter to \var{target}.
 \end{opcodedesc}
 
 \begin{opcodedesc}{FOR_ITER}{delta}
-\code{TOS} is an iterator.  Call its \method{next()} method.  If this
-yields a new value, push it on the stack (leaving the iterator below
-it).  If the iterator indicates it is exhausted  \code{TOS} is
-popped, and the byte code counter is incremented by \var{delta}.
+  \code{TOS} is an iterator.  Call its \method{__next__()} method.  If this
+  yields a new value, push it on the stack (leaving the iterator below it).  If
+  the iterator indicates it is exhausted \code{TOS} is popped, and the byte code
+  counter is incremented by \var{delta}.
 \end{opcodedesc}
 
 %\begin{opcodedesc}{FOR_LOOP}{delta}

Doc/lib/libexcs.tex

@@ -265,8 +265,8 @@ Raised when an \keyword{assert} statement fails.
 \end{excdesc}
 
 \begin{excdesc}{StopIteration}
-  Raised by an iterator's \method{next()} method to signal that there
-  are no further values.
+  Raised by builtin \function{next()} and an iterator's \method{__next__()}
+  method to signal that there are no further values.
   This is derived from \exception{Exception} rather than
   \exception{StandardError}, since this is not considered an error in
   its normal application.

Doc/lib/libfuncs.tex

@@ -342,14 +342,12 @@ class C:
 \end{funcdesc}
 
 \begin{funcdesc}{enumerate}{iterable}
-  Return an enumerate object. \var{iterable} must be a sequence, an
-  iterator, or some other object which supports iteration.  The
-  \method{next()} method of the iterator returned by
-  \function{enumerate()} returns a tuple containing a count (from
-  zero) and the corresponding value obtained from iterating over
-  \var{iterable}.  \function{enumerate()} is useful for obtaining an
-  indexed series: \code{(0, seq[0])}, \code{(1, seq[1])}, \code{(2,
-  seq[2])}, \ldots.
+  Return an enumerate object. \var{iterable} must be a sequence, an iterator, or
+  some other object which supports iteration.  The \method{__next__()} method of
+  the iterator returned by \function{enumerate()} returns a tuple containing a
+  count (from zero) and the corresponding value obtained from iterating over
+  \var{iterable}.  \function{enumerate()} is useful for obtaining an indexed
+  series: \code{(0, seq[0])}, \code{(1, seq[1])}, \code{(2, seq[2])}, \ldots.
   \versionadded{2.3}
 \end{funcdesc}
 
@@ -615,7 +613,7 @@ class C:
   support either of those protocols, \exception{TypeError} is raised.
   If the second argument, \var{sentinel}, is given, then \var{o} must
   be a callable object.  The iterator created in this case will call
-  \var{o} with no arguments for each call to its \method{next()}
+  \var{o} with no arguments for each call to its \method{__next__()}
   method; if the value returned is equal to \var{sentinel},
   \exception{StopIteration} will be raised, otherwise the value will
   be returned.
@@ -695,6 +693,12 @@ class C:
   \versionchanged[Added support for the optional \var{key} argument]{2.5}
 \end{funcdesc}
 
+\begin{funcdesc}{next}{iterator\optional{, default}}
+  Retrieve the next item from the \var{iterable} by calling its
+  \method{__next__()} method.  If \var{default} is given, it is returned if the
+  iterator is exhausted, otherwise \exception{StopIteration} is raised.
+\end{funcdesc}
+
 \begin{funcdesc}{object}{}
   Return a new featureless object.  \class{object} is a base
   for all new style classes.  It has the methods that are common

Doc/lib/libitertools.tex

@@ -164,16 +164,16 @@ by functions or loops that truncate the stream.
             self.tgtkey = self.currkey = self.currvalue = xrange(0)
         def __iter__(self):
             return self
-        def next(self):
+        def __next__(self):
             while self.currkey == self.tgtkey:
-                self.currvalue = self.it.next() # Exit on StopIteration
+                self.currvalue = next(self.it) # Exit on StopIteration
                 self.currkey = self.keyfunc(self.currvalue)
             self.tgtkey = self.currkey
             return (self.currkey, self._grouper(self.tgtkey))
         def _grouper(self, tgtkey):
             while self.currkey == tgtkey:
                 yield self.currvalue
-                self.currvalue = self.it.next() # Exit on StopIteration
+                self.currvalue = next(self.it) # Exit on StopIteration
                 self.currkey = self.keyfunc(self.currvalue)
   \end{verbatim}
   \versionadded{2.4}
@@ -227,7 +227,7 @@ by functions or loops that truncate the stream.
      def imap(function, *iterables):
          iterables = map(iter, iterables)
          while True:
-             args = [i.next() for i in iterables]
+             args = [next(i) for i in iterables]
              if function is None:
                  yield tuple(args)
              else:
@@ -253,11 +253,11 @@ by functions or loops that truncate the stream.
      def islice(iterable, *args):
          s = slice(*args)
          it = iter(xrange(s.start or 0, s.stop or sys.maxint, s.step or 1))
-         nexti = it.next()
+         nexti = next(it)
          for i, element in enumerate(iterable):
              if i == nexti:
                  yield element
-                 nexti = it.next()          
+                 nexti = next(it)
   \end{verbatim}
 
   If \var{start} is \code{None}, then iteration starts at zero.
@@ -276,7 +276,7 @@ by functions or loops that truncate the stream.
      def izip(*iterables):
          iterables = map(iter, iterables)
          while iterables:
-             result = [it.next() for it in iterables]
+             result = [next(it) for it in iterables]
              yield tuple(result)
   \end{verbatim}
 
@@ -297,7 +297,7 @@ by functions or loops that truncate the stream.
   from each iterator in-turn, but the process ends when one of the iterators
   terminates.  This leaves the last fetched values in limbo (they cannot be
   returned in a final, incomplete tuple and they are cannot be pushed back
-  into the iterator for retrieval with \code{it.next()}).  In general,
+  into the iterator for retrieval with \code{next(it)}).  In general,
   \function{izip()} should only be used with unequal length inputs when you
   don't care about trailing, unmatched values from the longer iterables.
 \end{funcdesc}
@@ -360,7 +360,7 @@ by functions or loops that truncate the stream.
      def starmap(function, iterable):
          iterable = iter(iterable)
          while True:
-             yield function(*iterable.next())
+             yield function(*next(iterable))
   \end{verbatim}
 \end{funcdesc}
 
@@ -393,7 +393,7 @@ by functions or loops that truncate the stream.
                      item = data.pop(i)
                  yield item
          it = iter(iterable)
-         return (gen(it.next), gen(it.next))
+         return (gen(it.__next__), gen(it.__next__))
   \end{verbatim}
 
   Note, once \function{tee()} has made a split, the original \var{iterable}
@@ -556,10 +556,7 @@ def repeatfunc(func, times=None, *args):
 def pairwise(iterable):
     "s -> (s0,s1), (s1,s2), (s2, s3), ..."
     a, b = tee(iterable)
-    try:
-        b.next()
-    except StopIteration:
-        pass
+    next(b, None)
     return izip(a, b)
 
 def grouper(n, iterable, padvalue=None):

Doc/lib/libstdtypes.tex

@@ -388,18 +388,17 @@ general and specific sequence types, dictionaries, and other more
 specialized forms.  The specific types are not important beyond their
 implementation of the iterator protocol.
 
-The intention of the protocol is that once an iterator's
-\method{next()} method raises \exception{StopIteration}, it will
-continue to do so on subsequent calls.  Implementations that
-do not obey this property are deemed broken.  (This constraint
-was added in Python 2.3; in Python 2.2, various iterators are
-broken according to this rule.)
+The intention of the protocol is that once an iterator's \method{__next__()}
+method raises \exception{StopIteration}, it will continue to do so on subsequent
+calls.  Implementations that do not obey this property are deemed broken.  (This
+constraint was added in Python 2.3; in Python 2.2, various iterators are broken
+according to this rule.)
 
-Python's generators provide a convenient way to implement the
-iterator protocol.  If a container object's \method{__iter__()}
-method is implemented as a generator, it will automatically
-return an iterator object (technically, a generator object)
-supplying the \method{__iter__()} and \method{next()} methods.
+Python's generators provide a convenient way to implement the iterator protocol.
+If a container object's \method{__iter__()} method is implemented as a
+generator, it will automatically return an iterator object (technically, a
+generator object) supplying the \method{__iter__()} and \method{__next__()}
+methods.
 
 
 \section{Sequence Types ---
@@ -1587,17 +1586,17 @@ finally:
   with a real file, this method should \emph{not} be implemented.}
 \end{methoddesc}
 
-\begin{methoddesc}[file]{next}{}
+\begin{methoddesc}[file]{__next__}{}
 A file object is its own iterator, for example \code{iter(\var{f})} returns
 \var{f} (unless \var{f} is closed).  When a file is used as an
 iterator, typically in a \keyword{for} loop (for example,
-\code{for line in f: print line}), the \method{next()} method is
+\code{for line in f: print line}), the \method{__next__()} method is
 called repeatedly.  This method returns the next input line, or raises
 \exception{StopIteration} when \EOF{} is hit.  In order to make a
 \keyword{for} loop the most efficient way of looping over the lines of
-a file (a very common operation), the \method{next()} method uses a
+a file (a very common operation), the \method{__next__()} method uses a
 hidden read-ahead buffer.  As a consequence of using a read-ahead
-buffer, combining \method{next()} with other file methods (like
+buffer, combining \method{__next__()} with other file methods (like
 \method{readline()}) does not work right.  However, using
 \method{seek()} to reposition the file to an absolute position will
 flush the read-ahead buffer.

Doc/lib/sqlite3/executemany_1.py

@@ -7,7 +7,7 @@ class IterChars:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         if self.count > ord('z'):
             raise StopIteration
         self.count += 1

Doc/ref/ref3.tex

@@ -633,7 +633,7 @@ A function or method which uses the \keyword{yield} statement (see
 section~\ref{yield}, ``The \keyword{yield} statement'') is called a
 \dfn{generator function}.  Such a function, when called, always
 returns an iterator object which can be used to execute the body of
-the function:  calling the iterator's \method{next()} method will
+the function:  calling the iterator's \method{__next__()} method will
 cause the function to execute until it provides a value using the
 \keyword{yield} statement.  When the function executes a
 \keyword{return} statement or falls off the end, a

Doc/ref/ref5.tex

@@ -222,7 +222,7 @@ evaluating the expression to yield a value that is reached the
 innermost block for each iteration.
 
 Variables used in the generator expression are evaluated lazily
-when the \method{next()} method is called for generator object
+when the \method{__next__()} method is called for generator object
 (in the same fashion as normal generators). However, the leftmost
 \keyword{for} clause is immediately evaluated so that error produced
 by it can be seen before any other possible error in the code that

Doc/ref/ref6.tex

@@ -418,19 +418,18 @@ Using a \keyword{yield} statement in a function definition is
 sufficient to cause that definition to create a generator function
 instead of a normal function.
 
-When a generator function is called, it returns an iterator known as a
-generator iterator, or more commonly, a generator.  The body of the
-generator function is executed by calling the generator's
-\method{next()} method repeatedly until it raises an exception.
+When a generator function is called, it returns an iterator known as a generator
+iterator, or more commonly, a generator.  The body of the generator function is
+executed by calling the generator's \method{__next__()} method repeatedly until
+it raises an exception.
 
-When a \keyword{yield} statement is executed, the state of the
-generator is frozen and the value of \grammartoken{expression_list} is
-returned to \method{next()}'s caller.  By ``frozen'' we mean that all
-local state is retained, including the current bindings of local
-variables, the instruction pointer, and the internal evaluation stack:
-enough information is saved so that the next time \method{next()} is
-invoked, the function can proceed exactly as if the \keyword{yield}
-statement were just another external call.
+When a \keyword{yield} statement is executed, the state of the generator is
+frozen and the value of \grammartoken{expression_list} is returned to
+\method{__next__()}'s caller.  By ``frozen'' we mean that all local state is
+retained, including the current bindings of local variables, the instruction
+pointer, and the internal evaluation stack: enough information is saved so that
+the next time \method{__next__()} is invoked, the function can proceed exactly
+as if the \keyword{yield} statement were just another external call.
 
 As of Python version 2.5, the \keyword{yield} statement is now
 allowed in the \keyword{try} clause of a \keyword{try} ...\ 

Doc/tut/glossary.tex

@@ -117,7 +117,7 @@ contain one or more {}\keyword{for} or \keyword{while} loops that
 \keyword{yield} elements back to the caller.  The function execution is
 stopped at the {}\keyword{yield} keyword (returning the result) and is
 resumed there when the next element is requested by calling the
-\method{next()} method of the returned iterator.
+\method{__next__()} method of the returned iterator.
 
 \index{generator expression}
 \item[generator expression]
@@ -207,10 +207,10 @@ hold the iterator for the duration of the loop.  See also
 \index{iterator}
 \item[iterator]
 An object representing a stream of data.  Repeated calls to the
-iterator's \method{next()} method return successive items in the
+iterator's \method{__next__()} method return successive items in the
 stream.  When no more data is available a \exception{StopIteration}
 exception is raised instead.  At this point, the iterator object is
-exhausted and any further calls to its \method{next()} method just
+exhausted and any further calls to its \method{__next__()} method just
 raise \exception{StopIteration} again.  Iterators are required to have
 an \method{__iter__()} method that returns the iterator object
 itself so every iterator is also iterable and may be used in most

Doc/tut/tut.tex

@@ -4488,34 +4488,35 @@ This style of access is clear, concise, and convenient.  The use of iterators
 pervades and unifies Python.  Behind the scenes, the \keyword{for}
 statement calls \function{iter()} on the container object.  The
 function returns an iterator object that defines the method
-\method{next()} which accesses elements in the container one at a
-time.  When there are no more elements, \method{next()} raises a
+\method{__next__()} which accesses elements in the container one at a
+time.  When there are no more elements, \method{__next__()} raises a
 \exception{StopIteration} exception which tells the \keyword{for} loop
-to terminate.  This example shows how it all works:
+to terminate.  You can call the \method{__next__()} method using the
+\function{next()} builtin; this example shows how it all works:
 
 \begin{verbatim}
 >>> s = 'abc'
 >>> it = iter(s)
 >>> it
 <iterator object at 0x00A1DB50>
->>> it.next()
+>>> next(it)
 'a'
->>> it.next()
+>>> next(it)
 'b'
->>> it.next()
+>>> next(it)
 'c'
->>> it.next()
+>>> next(it)
 
 Traceback (most recent call last):
   File "<stdin>", line 1, in ?
-    it.next()
+    next(it)
 StopIteration
 \end{verbatim}
 
 Having seen the mechanics behind the iterator protocol, it is easy to add
 iterator behavior to your classes.  Define a \method{__iter__()} method
-which returns an object with a \method{next()} method.  If the class defines
-\method{next()}, then \method{__iter__()} can just return \code{self}:
+which returns an object with a \method{__next__()} method.  If the class defines
+\method{__next__()}, then \method{__iter__()} can just return \code{self}:
 
 \begin{verbatim}
 class Reverse:
@@ -4525,7 +4526,7 @@ class Reverse:
         self.index = len(data)
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.index == 0:
             raise StopIteration
         self.index = self.index - 1
@@ -4545,7 +4546,7 @@ s
 
 Generators are a simple and powerful tool for creating iterators.  They are
 written like regular functions but use the \keyword{yield} statement whenever
-they want to return data.  Each time \method{next()} is called, the
+they want to return data.  Each time \function{next()} is called on it, the
 generator resumes where it left-off (it remembers all the data values and
 which statement was last executed).  An example shows that generators can
 be trivially easy to create:
@@ -4566,7 +4567,7 @@ g
 
 Anything that can be done with generators can also be done with class based
 iterators as described in the previous section.  What makes generators so
-compact is that the \method{__iter__()} and \method{next()} methods are
+compact is that the \method{__iter__()} and \method{__next__()} methods are
 created automatically.
 
 Another key feature is that the local variables and execution state

Lib/StringIO.py

@@ -64,10 +64,10 @@ class StringIO:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         """A file object is its own iterator, for example iter(f) returns f
         (unless f is closed). When a file is used as an iterator, typically
-        in a for loop (for example, for line in f: print line), the next()
+        in a for loop (for example, for line in f: print line), the __next__()
         method is called repeatedly. This method returns the next input line,
         or raises StopIteration when EOF is hit.
         """

Lib/UserDict.py

@@ -139,7 +139,7 @@ class DictMixin:
         return value
     def popitem(self):
         try:
-            k, v = self.iteritems().next()
+            k, v = next(self.iteritems())
         except StopIteration:
             raise KeyError, 'container is empty'
         del self[k]

Lib/codecs.py

@@ -600,7 +600,7 @@ class StreamReader(Codec):
         self.reset()
         self.stream.seek(offset, whence)
 
-    def next(self):
+    def __next__(self):
 
         """ Return the next decoded line from the input stream."""
         line = self.readline()
@@ -669,10 +669,10 @@ class StreamReaderWriter:
 
         return self.reader.readlines(sizehint)
 
-    def next(self):
+    def __next__(self):
 
         """ Return the next decoded line from the input stream."""
-        return self.reader.next()
+        return next(self.reader)
 
     def __iter__(self):
         return self
@@ -782,10 +782,10 @@ class StreamRecoder:
         data, bytesencoded = self.encode(data, self.errors)
         return data.splitlines(1)
 
-    def next(self):
+    def __next__(self):
 
         """ Return the next decoded line from the input stream."""
-        data = self.reader.next()
+        data = next(self.reader)
         data, bytesencoded = self.encode(data, self.errors)
         return data
 

Lib/contextlib.py

@@ -12,14 +12,14 @@ class GeneratorContextManager(object):
 
     def __enter__(self):
         try:
-            return self.gen.next()
+            return next(self.gen)
         except StopIteration:
             raise RuntimeError("generator didn't yield")
 
     def __exit__(self, type, value, traceback):
         if type is None:
             try:
-                self.gen.next()
+                next(self.gen)
             except StopIteration:
                 return
             else:

Lib/csv.py

@@ -79,17 +79,17 @@ class DictReader:
     def __iter__(self):
         return self
 
-    def next(self):
-        row = self.reader.next()
+    def __next__(self):
+        row = next(self.reader)
         if self.fieldnames is None:
             self.fieldnames = row
-            row = self.reader.next()
+            row = next(self.reader)
 
         # unlike the basic reader, we prefer not to return blanks,
         # because we will typically wind up with a dict full of None
         # values
         while row == []:
-            row = self.reader.next()
+            row = next(self.reader)
         d = dict(zip(self.fieldnames, row))
         lf = len(self.fieldnames)
         lr = len(row)
@@ -351,7 +351,7 @@ class Sniffer:
 
         rdr = reader(StringIO(sample), self.sniff(sample))
 
-        header = rdr.next() # assume first row is header
+        header = next(rdr) # assume first row is header
 
         columns = len(header)
         columnTypes = {}

Lib/difflib.py

@@ -1430,7 +1430,7 @@ def _mdiff(fromlines, tolines, context=None, linejunk=None,
             # so we can do some very readable comparisons.
             while len(lines) < 4:
                 try:
-                    lines.append(diff_lines_iterator.next())
+                    lines.append(next(diff_lines_iterator))
                 except StopIteration:
                     lines.append('X')
             s = ''.join([line[0] for line in lines])
@@ -1517,7 +1517,7 @@ def _mdiff(fromlines, tolines, context=None, linejunk=None,
         while True:
             # Collecting lines of text until we have a from/to pair
             while (len(fromlines)==0 or len(tolines)==0):
-                from_line, to_line, found_diff =line_iterator.next()
+                from_line, to_line, found_diff = next(line_iterator)
                 if from_line is not None:
                     fromlines.append((from_line,found_diff))
                 if to_line is not None:
@@ -1532,7 +1532,7 @@ def _mdiff(fromlines, tolines, context=None, linejunk=None,
     line_pair_iterator = _line_pair_iterator()
     if context is None:
         while True:
-            yield line_pair_iterator.next()
+            yield next(line_pair_iterator)
     # Handle case where user wants context differencing.  We must do some
     # storage of lines until we know for sure that they are to be yielded.
     else:
@@ -1545,7 +1545,7 @@ def _mdiff(fromlines, tolines, context=None, linejunk=None,
             index, contextLines = 0, [None]*(context)
             found_diff = False
             while(found_diff is False):
-                from_line, to_line, found_diff = line_pair_iterator.next()
+                from_line, to_line, found_diff = next(line_pair_iterator)
                 i = index % context
                 contextLines[i] = (from_line, to_line, found_diff)
                 index += 1
@@ -1565,7 +1565,7 @@ def _mdiff(fromlines, tolines, context=None, linejunk=None,
             # Now yield the context lines after the change
             lines_to_write = context-1
             while(lines_to_write):
-                from_line, to_line, found_diff = line_pair_iterator.next()
+                from_line, to_line, found_diff = next(line_pair_iterator)
                 # If another change within the context, extend the context
                 if found_diff:
                     lines_to_write = context-1

Lib/email/feedparser.py

@@ -122,7 +122,7 @@ class BufferedSubFile(object):
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         line = self.readline()
         if line == '':
             raise StopIteration
@@ -138,7 +138,7 @@ class FeedParser:
         self._factory = _factory
         self._input = BufferedSubFile()
         self._msgstack = []
-        self._parse = self._parsegen().next
+        self._parse = self._parsegen().__next__
         self._cur = None
         self._last = None
         self._headersonly = False

Lib/fileinput.py

@@ -240,7 +240,7 @@ class FileInput:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         try:
             line = self._buffer[self._bufindex]
         except IndexError:
@@ -259,7 +259,7 @@ class FileInput:
         if i != self._lineno:
             raise RuntimeError, "accessing lines out of order"
         try:
-            return self.next()
+            return self.__next__()
         except StopIteration:
             raise IndexError, "end of input reached"
 

Lib/gzip.py

@@ -453,7 +453,7 @@ class GzipFile:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         line = self.readline()
         if line:
             return line

Lib/heapq.py

@@ -325,7 +325,7 @@ def merge(*iterables):
     h_append = h.append
     for itnum, it in enumerate(map(iter, iterables)):
         try:
-            next = it.next
+            next = it.__next__
             h_append([next(), itnum, next])
         except _StopIteration:
             pass

Lib/hotshot/log.py

@@ -29,7 +29,7 @@ class LogReader:
         self._funcmap = {}
 
         self._reader = _hotshot.logreader(logfn)
-        self._nextitem = self._reader.next
+        self._nextitem = self._reader.__next__
         self._info = self._reader.info
         if 'current-directory' in self._info:
             self.cwd = self._info['current-directory']
@@ -93,7 +93,7 @@ class LogReader:
     # same bound method can be used as the __getitem__() method -- this
     # avoids using an additional method call which kills the performance.
 
-    def next(self, index=0):
+    def __next__(self, index=0):
         while 1:
             # This call may raise StopIteration:
             what, tdelta, fileno, lineno = self._nextitem()

Lib/httplib.py

@@ -1098,7 +1098,7 @@ class SSLFile(SharedSocketClient):
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         line = self.readline()
         if not line:
             raise StopIteration

Lib/inspect.py

@@ -603,7 +603,7 @@ def getblock(lines):
     """Extract the block of code at the top of the given list of lines."""
     blockfinder = BlockFinder()
     try:
-        tokenize.tokenize(iter(lines).next, blockfinder.tokeneater)
+        tokenize.tokenize(iter(lines).__next__, blockfinder.tokeneater)
     except (EndOfBlock, IndentationError):
         pass
     return lines[:blockfinder.last]

Lib/io.py

@@ -904,7 +904,7 @@ class TextIOBase(IOBase):
         """
         return self
 
-    def next(self) -> str:
+    def __next__(self) -> str:
         """Same as readline() except raises StopIteration on immediate EOF."""
         line = self.readline()
         if not line:
@@ -1125,7 +1125,7 @@ class TextIOWrapper(TextIOBase):
             self._pending = res[n:]
             return self._simplify(res[:n])
 
-    def next(self) -> str:
+    def __next__(self) -> str:
         self._telling = False
         line = self.readline()
         if not line:

Lib/mailbox.py

@@ -480,7 +480,7 @@ class Maildir(Mailbox):
             self._onetime_keys = iter(self.keys())
         while True:
             try:
-                return self[self._onetime_keys.next()]
+                return self[next(self._onetime_keys)]
             except StopIteration:
                 return None
             except KeyError:

Lib/pickle.py

@@ -640,7 +640,7 @@ class Pickler:
             tmp = []
             for i in r:
                 try:
-                    x = items.next()
+                    x = next(items)
                     tmp.append(x)
                 except StopIteration:
                     items = None
@@ -688,7 +688,7 @@ class Pickler:
             tmp = []
             for i in r:
                 try:
-                    tmp.append(items.next())
+                    tmp.append(next(items))
                 except StopIteration:
                     items = None
                     break

Lib/pstats.py

@@ -396,7 +396,7 @@ class Stats:
         subheader = False
         for cc, nc, tt, ct, callers in self.stats.values():
             if callers:
-                value = iter(callers.values()).next()
+                value = next(iter(callers.values()))
                 subheader = isinstance(value, tuple)
                 break
         if subheader:

Lib/pyclbr.py

@@ -161,7 +161,7 @@ def _readmodule(module, path, inpackage=None):
                 # close previous nested classes and defs
                 while stack and stack[-1][1] >= thisindent:
                     del stack[-1]
-                tokentype, meth_name, start, end, line = g.next()
+                tokentype, meth_name, start, end, line = next(g)
                 if tokentype != NAME:
                     continue # Syntax error
                 if stack:
@@ -179,11 +179,11 @@ def _readmodule(module, path, inpackage=None):
                 # close previous nested classes and defs
                 while stack and stack[-1][1] >= thisindent:
                     del stack[-1]
-                tokentype, class_name, start, end, line = g.next()
+                tokentype, class_name, start, end, line = next(g)
                 if tokentype != NAME:
                     continue # Syntax error
                 # parse what follows the class name
-                tokentype, token, start, end, line = g.next()
+                tokentype, token, start, end, line = next(g)
                 inherit = None
                 if token == '(':
                     names = [] # List of superclasses
@@ -191,7 +191,7 @@ def _readmodule(module, path, inpackage=None):
                     level = 1
                     super = [] # Tokens making up current superclass
                     while True:
-                        tokentype, token, start, end, line = g.next()
+                        tokentype, token, start, end, line = next(g)
                         if token in (')', ',') and level == 1:
                             n = "".join(super)
                             if n in dict:
@@ -287,7 +287,7 @@ def _getnamelist(g):
             name2 = None
         names.append((name, name2))
         while token != "," and "\n" not in token:
-            tokentype, token, start, end, line = g.next()
+            tokentype, token, start, end, line = next(g)
         if token != ",":
             break
     return names
@@ -297,15 +297,15 @@ def _getname(g):
     # name is the dotted name, or None if there was no dotted name,
     # and token is the next input token.
     parts = []
-    tokentype, token, start, end, line = g.next()
+    tokentype, token, start, end, line = next(g)
     if tokentype != NAME and token != '*':
         return (None, token)
     parts.append(token)
     while True:
-        tokentype, token, start, end, line = g.next()
+        tokentype, token, start, end, line = next(g)
         if token != '.':
             break
-        tokentype, token, start, end, line = g.next()
+        tokentype, token, start, end, line = next(g)
         if tokentype != NAME:
             break
         parts.append(token)

Lib/shelve.py

@@ -174,7 +174,7 @@ class BsdDbShelf(Shelf):
         return (key, Unpickler(f).load())
 
     def next(self):
-        (key, value) = self.dict.next()
+        (key, value) = next(self.dict)
         f = StringIO(value)
         return (key, Unpickler(f).load())
 

Lib/shlex.py

@@ -265,7 +265,7 @@ class shlex:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         token = self.get_token()
         if token == self.eof:
             raise StopIteration

Lib/socket.py

@@ -409,7 +409,7 @@ class _fileobject(object):
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         line = self.readline()
         if not line:
             raise StopIteration

Lib/sqlite3/test/dbapi.py

@@ -286,7 +286,7 @@ class CursorTests(unittest.TestCase):
             def __init__(self):
                 self.value = 5
 
-            def next(self):
+            def __next__(self):
                 if self.value == 10:
                     raise StopIteration
                 else:

Lib/tarfile.py

@@ -2046,7 +2046,7 @@ class TarIter:
         """Return iterator object.
         """
         return self
-    def next(self):
+    def __next__(self):
         """Return the next item using TarFile's next() method.
            When all members have been read, set TarFile as _loaded.
         """

Lib/tempfile.py

@@ -124,7 +124,7 @@ class _RandomNameSequence:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         m = self.mutex
         c = self.characters
         choose = self.rng.choice
@@ -191,7 +191,7 @@ def _get_default_tempdir():
             dir = _os.path.normcase(_os.path.abspath(dir))
         # Try only a few names per directory.
         for seq in xrange(100):
-            name = namer.next()
+            name = next(namer)
             filename = _os.path.join(dir, name)
             try:
                 fd = _os.open(filename, flags, 0600)
@@ -230,7 +230,7 @@ def _mkstemp_inner(dir, pre, suf, flags):
     names = _get_candidate_names()
 
     for seq in xrange(TMP_MAX):
-        name = names.next()
+        name = next(names)
         file = _os.path.join(dir, pre + name + suf)
         try:
             fd = _os.open(file, flags, 0600)
@@ -322,7 +322,7 @@ def mkdtemp(suffix="", prefix=template, dir=None):
     names = _get_candidate_names()
 
     for seq in xrange(TMP_MAX):
-        name = names.next()
+        name = next(names)
         file = _os.path.join(dir, prefix + name + suffix)
         try:
             _os.mkdir(file, 0700)
@@ -357,7 +357,7 @@ def mktemp(suffix="", prefix=template, dir=None):
 
     names = _get_candidate_names()
     for seq in xrange(TMP_MAX):
-        name = names.next()
+        name = next(names)
         file = _os.path.join(dir, prefix + name + suffix)
         if not _exists(file):
             return file

Lib/test/list_tests.py

@@ -77,7 +77,7 @@ class CommonTest(seq_tests.CommonTest):
         a = self.type2test(range(20))
         r = reversed(a)
         self.assertEqual(list(r), self.type2test(range(19, -1, -1)))
-        self.assertRaises(StopIteration, r.next)
+        self.assertRaises(StopIteration, next, r)
         self.assertEqual(list(reversed(self.type2test())),
                          self.type2test())
 

Lib/test/mapping_tests.py

@@ -69,7 +69,7 @@ class BasicTestMappingProtocol(unittest.TestCase):
         if not d: self.fail("Full mapping must compare to True")
         # keys(), items(), iterkeys() ...
         def check_iterandlist(iter, lst, ref):
-            self.assert_(hasattr(iter, 'next'))
+            self.assert_(hasattr(iter, '__next__'))
             self.assert_(hasattr(iter, '__iter__'))
             x = list(iter)
             self.assert_(set(x)==set(lst)==set(ref))
@@ -81,8 +81,8 @@ class BasicTestMappingProtocol(unittest.TestCase):
         check_iterandlist(iter(d.items()), list(d.items()),
                           self.reference.items())
         #get
-        key, value = iter(d.items()).next()
-        knownkey, knownvalue = iter(self.other.items()).next()
+        key, value = next(iter(d.items()))
+        knownkey, knownvalue = next(iter(self.other.items()))
         self.assertEqual(d.get(key, knownvalue), value)
         self.assertEqual(d.get(knownkey, knownvalue), knownvalue)
         self.failIf(knownkey in d)
@@ -107,8 +107,8 @@ class BasicTestMappingProtocol(unittest.TestCase):
         self.assertEqual(dict(p), self.reference)
         d = self._full_mapping(self.reference)
         #setdefault
-        key, value = iter(d.items()).next()
-        knownkey, knownvalue = iter(self.other.items()).next()
+        key, value = next(iter(d.items()))
+        knownkey, knownvalue = next(iter(self.other.items()))
         self.assertEqual(d.setdefault(key, knownvalue), value)
         self.assertEqual(d[key], value)
         self.assertEqual(d.setdefault(knownkey, knownvalue), knownvalue)
@@ -225,7 +225,7 @@ class BasicTestMappingProtocol(unittest.TestCase):
                         self.i = 1
                     def __iter__(self):
                         return self
-                    def next(self):
+                    def __next__(self):
                         if self.i:
                             self.i = 0
                             return 'a'
@@ -242,7 +242,7 @@ class BasicTestMappingProtocol(unittest.TestCase):
                         self.i = ord('a')
                     def __iter__(self):
                         return self
-                    def next(self):
+                    def __next__(self):
                         if self.i <= ord('z'):
                             rtn = chr(self.i)
                             self.i += 1
@@ -257,7 +257,7 @@ class BasicTestMappingProtocol(unittest.TestCase):
         class badseq(object):
             def __iter__(self):
                 return self
-            def next(self):
+            def __next__(self):
                 raise Exc()
 
         self.assertRaises(Exc, d.update, badseq())
@@ -456,7 +456,7 @@ class TestMappingProtocol(BasicTestMappingProtocol):
         class BadSeq(object):
             def __iter__(self):
                 return self
-            def next(self):
+            def __next__(self):
                 raise Exc()
 
         self.assertRaises(Exc, self.type2test.fromkeys, BadSeq())

Lib/test/seq_tests.py

@@ -26,7 +26,7 @@ class IterFunc:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -46,14 +46,14 @@ class IterNextOnly:
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
         return v
 
 class IterNoNext:
-    'Iterator missing next()'
+    'Iterator missing __next__()'
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
@@ -67,7 +67,7 @@ class IterGenExc:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         3 // 0
 
 class IterFuncStop:
@@ -76,7 +76,7 @@ class IterFuncStop:
         pass
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         raise StopIteration
 
 from itertools import chain, imap
@@ -296,7 +296,7 @@ class CommonTest(unittest.TestCase):
         class T(self.type2test):
             def __getitem__(self, key):
                 return str(key) + '!!!'
-        self.assertEqual(iter(T((1,2))).next(), 1)
+        self.assertEqual(next(iter(T((1,2)))), 1)
 
     def test_repeat(self):
         for m in xrange(4):

Lib/test/test_StringIO.py

@@ -89,14 +89,14 @@ class TestGenericStringIO(unittest.TestCase):
         eq(iter(self._fp), self._fp)
         # Does this object support the iteration protocol?
         unless(hasattr(self._fp, '__iter__'))
-        unless(hasattr(self._fp, 'next'))
+        unless(hasattr(self._fp, '__next__'))
         i = 0
         for line in self._fp:
             eq(line, self._line + '\n')
             i += 1
         eq(i, 5)
         self._fp.close()
-        self.assertRaises(ValueError, self._fp.next)
+        self.assertRaises(ValueError, next, self._fp)
 
 class TestStringIO(TestGenericStringIO):
     MODULE = StringIO

Lib/test/test_bsddb.py

@@ -72,7 +72,7 @@ class TestBSDDB(unittest.TestCase):
         di = iter(self.d)
         while 1:
             try:
-                key = di.next()
+                key = next(di)
                 self.d[key] = 'modified '+key
             except StopIteration:
                 break
@@ -83,7 +83,7 @@ class TestBSDDB(unittest.TestCase):
         fi = iter(self.f)
         while 1:
             try:
-                key = fi.next()
+                key = next(fi)
                 self.f[key] = 'modified '+key
             except StopIteration:
                 break
@@ -97,7 +97,7 @@ class TestBSDDB(unittest.TestCase):
         di = iter(self.d.items())
         while 1:
             try:
-                k, v = di.next()
+                k, v = next(di)
                 self.d[k] = 'modified '+v
             except StopIteration:
                 break
@@ -108,7 +108,7 @@ class TestBSDDB(unittest.TestCase):
         fi = iter(self.f.items())
         while 1:
             try:
-                k, v = fi.next()
+                k, v = next(fi)
                 self.f[k] = 'modified '+v
             except StopIteration:
                 break
@@ -160,13 +160,13 @@ class TestBSDDB(unittest.TestCase):
         if hasattr(self.f, 'iteritems'):
             if debug: print("D")
             i = iter(self.f.items())
-            k,v = i.next()
+            k,v = next(i)
             if debug: print("E")
             self.f[k] = "please don't deadlock"
             if debug: print("F")
             while 1:
                 try:
-                    k,v = i.next()
+                    k,v = next(i)
                 except StopIteration:
                     break
             if debug: print("F2")
@@ -176,7 +176,7 @@ class TestBSDDB(unittest.TestCase):
             while i:
                 try:
                     if debug: print("H")
-                    k = i.next()
+                    k = next(i)
                     if debug: print("I")
                     self.f[k] = "deadlocks-r-us"
                     if debug: print("J")
@@ -201,7 +201,7 @@ class TestBSDDB(unittest.TestCase):
         i = iter(self.f.iteritems())
         nc2 = len(self.f._cursor_refs)
         # use the iterator (should run to the first yield, creating the cursor)
-        k, v = i.next()
+        k, v = next(i)
         nc3 = len(self.f._cursor_refs)
         # destroy the iterator; this should cause the weakref callback
         # to remove the cursor object from self.f._cursor_refs

Lib/test/test_builtin.py

@@ -907,9 +907,9 @@ class BuiltinTest(unittest.TestCase):
             lists.append(unicode("12"))
         for l in lists:
             i = iter(l)
-            self.assertEqual(i.next(), '1')
-            self.assertEqual(i.next(), '2')
-            self.assertRaises(StopIteration, i.next)
+            self.assertEqual(next(i), '1')
+            self.assertEqual(next(i), '2')
+            self.assertRaises(StopIteration, next, i)
 
     def test_isinstance(self):
         class C:
@@ -1305,6 +1305,33 @@ class BuiltinTest(unittest.TestCase):
         self.assertEqual(min(data, key=f),
                          sorted(data, key=f)[0])
 
+    def test_next(self):
+        it = iter(range(2))
+        self.assertEqual(next(it), 0)
+        self.assertEqual(next(it), 1)
+        self.assertRaises(StopIteration, next, it)
+        self.assertRaises(StopIteration, next, it)
+        self.assertEquals(next(it, 42), 42)
+
+        class Iter(object):
+            def __iter__(self):
+                return self
+            def __next__(self):
+                raise StopIteration
+
+        it = iter(Iter())
+        self.assertEquals(next(it, 42), 42)
+        self.assertRaises(StopIteration, next, it)
+
+        def gen():
+            yield 1
+            return
+
+        it = gen()
+        self.assertEquals(next(it), 1)
+        self.assertRaises(StopIteration, next, it)
+        self.assertEquals(next(it, 42), 42)
+
     def test_oct(self):
         self.assertEqual(oct(100), '0144')
         self.assertEqual(oct(100), '0144')

Lib/test/test_csv.py

@@ -271,13 +271,13 @@ class Test_Csv(unittest.TestCase):
     def test_read_linenum(self):
         r = csv.reader(['line,1', 'line,2', 'line,3'])
         self.assertEqual(r.line_num, 0)
-        r.next()
+        next(r)
         self.assertEqual(r.line_num, 1)
-        r.next()
+        next(r)
         self.assertEqual(r.line_num, 2)
-        r.next()
+        next(r)
         self.assertEqual(r.line_num, 3)
-        self.assertRaises(StopIteration, r.next)
+        self.assertRaises(StopIteration, next, r)
         self.assertEqual(r.line_num, 3)
 
 class TestDialectRegistry(unittest.TestCase):
@@ -338,9 +338,9 @@ class TestDialectRegistry(unittest.TestCase):
         try:
             fileobj.write("abc def\nc1ccccc1 benzene\n")
             fileobj.seek(0)
-            rdr = csv.reader(fileobj, dialect=space())
-            self.assertEqual(rdr.next(), ["abc", "def"])
-            self.assertEqual(rdr.next(), ["c1ccccc1", "benzene"])
+            reader = csv.reader(fileobj, dialect=space())
+            self.assertEqual(next(reader), ["abc", "def"])
+            self.assertEqual(next(reader), ["c1ccccc1", "benzene"])
         finally:
             fileobj.close()
             os.unlink(name)
@@ -593,7 +593,7 @@ class TestDictFields(unittest.TestCase):
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
                                     fieldnames=["f1", "f2", "f3"])
-            self.assertEqual(reader.next(), {"f1": '1', "f2": '2', "f3": 'abc'})
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
         finally:
             fileobj.close()
             os.unlink(name)
@@ -605,7 +605,7 @@ class TestDictFields(unittest.TestCase):
             fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj)
-            self.assertEqual(reader.next(), {"f1": '1', "f2": '2', "f3": 'abc'})
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
         finally:
             fileobj.close()
             os.unlink(name)
@@ -618,7 +618,7 @@ class TestDictFields(unittest.TestCase):
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
                                     fieldnames=["f1", "f2"])
-            self.assertEqual(reader.next(), {"f1": '1', "f2": '2',
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
                                              None: ["abc", "4", "5", "6"]})
         finally:
             fileobj.close()
@@ -632,7 +632,7 @@ class TestDictFields(unittest.TestCase):
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
                                     fieldnames=["f1", "f2"], restkey="_rest")
-            self.assertEqual(reader.next(), {"f1": '1', "f2": '2',
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
                                              "_rest": ["abc", "4", "5", "6"]})
         finally:
             fileobj.close()
@@ -645,7 +645,7 @@ class TestDictFields(unittest.TestCase):
             fileobj.write("f1,f2\r\n1,2,abc,4,5,6\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj, restkey="_rest")
-            self.assertEqual(reader.next(), {"f1": '1', "f2": '2',
+            self.assertEqual(next(reader), {"f1": '1', "f2": '2',
                                              "_rest": ["abc", "4", "5", "6"]})
         finally:
             fileobj.close()
@@ -660,9 +660,9 @@ class TestDictFields(unittest.TestCase):
             reader = csv.DictReader(fileobj,
                                     fieldnames="1 2 3 4 5 6".split(),
                                     restval="DEFAULT")
-            self.assertEqual(reader.next(), {"1": '1', "2": '2', "3": 'abc',
+            self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
                                              "4": '4', "5": '5', "6": '6'})
-            self.assertEqual(reader.next(), {"1": '1', "2": '2', "3": 'abc',
+            self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
                                              "4": 'DEFAULT', "5": 'DEFAULT',
                                              "6": 'DEFAULT'})
         finally:
@@ -678,7 +678,7 @@ class TestDictFields(unittest.TestCase):
 
         reader = csv.DictReader(sample,
                                 fieldnames="i1 float i2 s1 s2".split())
-        self.assertEqual(reader.next(), {"i1": '2147483648',
+        self.assertEqual(next(reader), {"i1": '2147483648',
                                          "float": '43.0e12',
                                          "i2": '17',
                                          "s1": 'abc',
@@ -688,16 +688,16 @@ class TestDictFields(unittest.TestCase):
         reader = csv.DictReader(["1,2,abc,4,5,6\r\n","\r\n",
                                  "1,2,abc,4,5,6\r\n"],
                                 fieldnames="1 2 3 4 5 6".split())
-        self.assertEqual(reader.next(), {"1": '1', "2": '2', "3": 'abc',
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
                                          "4": '4', "5": '5', "6": '6'})
-        self.assertEqual(reader.next(), {"1": '1', "2": '2', "3": 'abc',
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
                                          "4": '4', "5": '5', "6": '6'})
 
     def test_read_semi_sep(self):
         reader = csv.DictReader(["1;2;abc;4;5;6\r\n"],
                                 fieldnames="1 2 3 4 5 6".split(),
                                 delimiter=';')
-        self.assertEqual(reader.next(), {"1": '1', "2": '2', "3": 'abc',
+        self.assertEqual(next(reader), {"1": '1', "2": '2', "3": 'abc',
                                          "4": '4', "5": '5', "6": '6'})
 
 class TestArrayWrites(unittest.TestCase):

Lib/test/test_deque.py

@@ -394,13 +394,13 @@ class TestVariousIteratorArgs(unittest.TestCase):
         d = deque('abcdefg')
         it = iter(d)
         d.pop()
-        self.assertRaises(RuntimeError, it.next)
+        self.assertRaises(RuntimeError, next, it)
 
     def test_runtime_error_on_empty_deque(self):
         d = deque()
         it = iter(d)
         d.append(10)
-        self.assertRaises(RuntimeError, it.next)
+        self.assertRaises(RuntimeError, next, it)
 
 class Deque(deque):
     pass
@@ -567,7 +567,7 @@ deque(['a', 'b', 'd', 'e', 'f'])
 ...     while pending:
 ...         task = pending.popleft()
 ...         try:
-...             yield task.next()
+...             yield next(task)
 ...         except StopIteration:
 ...             continue
 ...         pending.append(task)

Lib/test/test_dict.py

@@ -144,7 +144,7 @@ class DictTest(unittest.TestCase):
                         self.i = 1
                     def __iter__(self):
                         return self
-                    def next(self):
+                    def __next__(self):
                         if self.i:
                             self.i = 0
                             return 'a'
@@ -161,7 +161,7 @@ class DictTest(unittest.TestCase):
                         self.i = ord('a')
                     def __iter__(self):
                         return self
-                    def next(self):
+                    def __next__(self):
                         if self.i <= ord('z'):
                             rtn = chr(self.i)
                             self.i += 1
@@ -175,7 +175,7 @@ class DictTest(unittest.TestCase):
         class badseq(object):
             def __iter__(self):
                 return self
-            def next(self):
+            def __next__(self):
                 raise Exc()
 
         self.assertRaises(Exc, {}.update, badseq())
@@ -225,7 +225,7 @@ class DictTest(unittest.TestCase):
         class BadSeq(object):
             def __iter__(self):
                 return self
-            def next(self):
+            def __next__(self):
                 raise Exc()
 
         self.assertRaises(Exc, dict.fromkeys, BadSeq())

Lib/test/test_difflib.py

@@ -16,9 +16,9 @@ class TestSFbugs(unittest.TestCase):
     def test_comparing_empty_lists(self):
         # Check fix for bug #979794
         group_gen = difflib.SequenceMatcher(None, [], []).get_grouped_opcodes()
-        self.assertRaises(StopIteration, group_gen.next)
+        self.assertRaises(StopIteration, next, group_gen)
         diff_gen = difflib.unified_diff([], [])
-        self.assertRaises(StopIteration, diff_gen.next)
+        self.assertRaises(StopIteration, next, diff_gen)
 
 patch914575_from1 = """
    1. Beautiful is beTTer than ugly.

Lib/test/test_enumerate.py

@@ -17,7 +17,7 @@ class I:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -37,7 +37,7 @@ class X:
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -50,11 +50,11 @@ class E:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         3 // 0
 
 class N:
-    'Iterator missing next()'
+    'Iterator missing __next__()'
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
@@ -76,17 +76,17 @@ class EnumerateTestCase(unittest.TestCase):
     def test_getitemseqn(self):
         self.assertEqual(list(self.enum(G(self.seq))), self.res)
         e = self.enum(G(''))
-        self.assertRaises(StopIteration, e.next)
+        self.assertRaises(StopIteration, next, e)
 
     def test_iteratorseqn(self):
         self.assertEqual(list(self.enum(I(self.seq))), self.res)
         e = self.enum(I(''))
-        self.assertRaises(StopIteration, e.next)
+        self.assertRaises(StopIteration, next, e)
 
     def test_iteratorgenerator(self):
         self.assertEqual(list(self.enum(Ig(self.seq))), self.res)
         e = self.enum(Ig(''))
-        self.assertRaises(StopIteration, e.next)
+        self.assertRaises(StopIteration, next, e)
 
     def test_noniterable(self):
         self.assertRaises(TypeError, self.enum, X(self.seq))

Lib/test/test_extcall.py

@@ -103,7 +103,7 @@ class Nothing:
         self.c = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.c == 4:
             raise StopIteration
         c = self.c

Lib/test/test_file.py

@@ -95,7 +95,7 @@ class AutoFileTests(unittest.TestCase):
         self.assert_(f.closed)
 
     def testMethods(self):
-        methods = ['fileno', 'flush', 'isatty', 'next', 'read', 'readinto',
+        methods = ['fileno', 'flush', 'isatty', '__next__', 'read', 'readinto',
                    'readline', 'readlines', 'seek', 'tell', 'truncate',
                    'write', '__iter__']
         if sys.platform.startswith('atheos'):
@@ -248,7 +248,7 @@ class OtherFileTests(unittest.TestCase):
             # Test for appropriate errors mixing read* and iteration
             for methodname, args in methods:
                 f = open(TESTFN, 'rb')
-                if f.next() != filler:
+                if next(f) != filler:
                     self.fail, "Broken testfile"
                 meth = getattr(f, methodname)
                 try:
@@ -269,7 +269,7 @@ class OtherFileTests(unittest.TestCase):
             # between 4 and 16384 (inclusive).
             f = open(TESTFN, 'rb')
             for i in range(nchunks):
-                f.next()
+                next(f)
             testline = testlines.pop(0)
             try:
                 line = f.readline()

Lib/test/test_fileinput.py

@@ -179,7 +179,7 @@ try:
     t2 = writeTmp(2, ["C\nD"])
     fi = FileInput(files=(t1, t2))
     verify(fi.fileno() == -1)
-    line = fi.next()
+    line = next(fi)
     verify(fi.fileno() != -1)
     fi.nextfile()
     verify(fi.fileno() == -1)

Lib/test/test_generators.py

@@ -10,14 +10,14 @@ Let's try a simple generator:
     1
     2
     >>> g = f()
-    >>> g.next()
+    >>> next(g)
     1
-    >>> g.next()
+    >>> next(g)
     2
 
 "Falling off the end" stops the generator:
 
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
       File "<stdin>", line 2, in g
@@ -31,14 +31,14 @@ Let's try a simple generator:
     ...     yield 2 # never reached
     ...
     >>> g = f()
-    >>> g.next()
+    >>> next(g)
     1
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
       File "<stdin>", line 3, in f
     StopIteration
-    >>> g.next() # once stopped, can't be resumed
+    >>> next(g) # once stopped, can't be resumed
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
@@ -51,13 +51,13 @@ Let's try a simple generator:
     ...     yield 2 # never reached
     ...
     >>> g = f()
-    >>> g.next()
+    >>> next(g)
     1
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
@@ -105,7 +105,7 @@ Generators always return to the most recent caller:
 
     >>> def creator():
     ...     r = yrange(5)
-    ...     print("creator", r.next())
+    ...     print("creator", next(r))
     ...     return r
     ...
     >>> def caller():
@@ -141,10 +141,10 @@ Specification:  Yield
     running:
 
     >>> def g():
-    ...     i = me.next()
+    ...     i = next(me)
     ...     yield i
     >>> me = g()
-    >>> me.next()
+    >>> next(me)
     Traceback (most recent call last):
      ...
       File "<string>", line 2, in g
@@ -185,13 +185,13 @@ Specification: Generators and Exception Propagation
     ...     yield f()  # the zero division exception propagates
     ...     yield 42   # and we'll never get here
     >>> k = g()
-    >>> k.next()
+    >>> next(k)
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
       File "<stdin>", line 2, in g
       File "<stdin>", line 2, in f
     ZeroDivisionError: integer division or modulo by zero
-    >>> k.next()  # and the generator cannot be resumed
+    >>> next(k)  # and the generator cannot be resumed
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
@@ -382,9 +382,9 @@ From the Iterators list, about the types of these things.
 >>> type(i)
 <type 'generator'>
 >>> [s for s in dir(i) if not s.startswith('_')]
-['close', 'gi_frame', 'gi_running', 'next', 'send', 'throw']
->>> print(i.next.__doc__)
-x.next() -> the next value, or raise StopIteration
+['close', 'gi_frame', 'gi_running', 'send', 'throw']
+>>> print(i.__next__.__doc__)
+x.__next__() <==> next(x)
 >>> iter(i) is i
 True
 >>> import types
@@ -406,7 +406,7 @@ AttributeError: readonly attribute
 >>> me = g()
 >>> me.gi_running
 0
->>> me.next()
+>>> next(me)
 1
 >>> me.gi_running
 0
@@ -429,7 +429,7 @@ Subject: Re: PEP 255: Simple Generators
 ...             yield x
 ...
 ...     def find(self):
-...         return self.generator.next()
+...         return next(self.generator)
 ...
 ...     def union(self, parent):
 ...         if self.parent:
@@ -493,7 +493,7 @@ fun_tests = """
 Build up to a recursive Sieve of Eratosthenes generator.
 
 >>> def firstn(g, n):
-...     return [g.next() for i in range(n)]
+...     return [next(g) for i in range(n)]
 
 >>> def intsfrom(i):
 ...     while 1:
@@ -512,7 +512,7 @@ Build up to a recursive Sieve of Eratosthenes generator.
 [1, 2, 4, 5, 7, 8]
 
 >>> def sieve(ints):
-...     prime = ints.next()
+...     prime = next(ints)
 ...     yield prime
 ...     not_divisible_by_prime = exclude_multiples(prime, ints)
 ...     for p in sieve(not_divisible_by_prime):
@@ -536,19 +536,19 @@ Try writing it without generators, and correctly, and without generating
 [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
 
 >>> def merge(g, h):
-...     ng = g.next()
-...     nh = h.next()
+...     ng = next(g)
+...     nh = next(h)
 ...     while 1:
 ...         if ng < nh:
 ...             yield ng
-...             ng = g.next()
+...             ng = next(g)
 ...         elif ng > nh:
 ...             yield nh
-...             nh = h.next()
+...             nh = next(h)
 ...         else:
 ...             yield ng
-...             ng = g.next()
-...             nh = h.next()
+...             ng = next(g)
+...             nh = next(h)
 
 The following works, but is doing a whale of a lot of redundant work --
 it's not clear how to get the internal uses of m235 to share a single
@@ -589,7 +589,7 @@ arguments are iterable -- a LazyList is the same as a generator to times().
 >>> class LazyList:
 ...     def __init__(self, g):
 ...         self.sofar = []
-...         self.fetch = g.next
+...         self.fetch = g.__next__
 ...
 ...     def __getitem__(self, i):
 ...         sofar, fetch = self.sofar, self.fetch
@@ -626,10 +626,10 @@ Ye olde Fibonacci generator, LazyList style.
 ...
 ...     def sum(g, h):
 ...         while 1:
-...             yield g.next() + h.next()
+...             yield next(g) + next(h)
 ...
 ...     def tail(g):
-...         g.next()    # throw first away
+...         next(g)    # throw first away
 ...         for x in g:
 ...             yield x
 ...
@@ -705,12 +705,12 @@ Ye olde Fibonacci generator, tee style.
 ...
 ...     def _isum(g, h):
 ...         while 1:
-...             yield g.next() + h.next()
+...             yield next(g) + next(h)
 ...
 ...     def _fib():
 ...         yield 1
 ...         yield 2
-...         fibTail.next() # throw first away
+...         next(fibTail) # throw first away
 ...         for res in _isum(fibHead, fibTail):
 ...             yield res
 ...
@@ -890,13 +890,13 @@ This one caused a crash (see SF bug 567538):
 ...             yield i
 ...
 >>> g = f()
->>> print(g.next())
+>>> print(next(g))
 0
->>> print(g.next())
+>>> print(next(g))
 1
->>> print(g.next())
+>>> print(next(g))
 2
->>> print(g.next())
+>>> print(next(g))
 Traceback (most recent call last):
 StopIteration
 """
@@ -1013,7 +1013,7 @@ def flat_conjoin(gs):  # rename to conjoin to run tests with this instead
         # Descend.
         try:
             while i < n:
-                it = iters[i] = gs[i]().next
+                it = iters[i] = gs[i]().__next__
                 values[i] = it()
                 i += 1
         except _StopIteration:
@@ -1463,7 +1463,7 @@ Sending a value into a started generator:
 ...     print((yield 1))
 ...     yield 2
 >>> g = f()
->>> g.next()
+>>> next(g)
 1
 >>> g.send(42)
 42
@@ -1506,7 +1506,7 @@ A yield expression with augmented assignment.
 ...         seq.append(count)
 >>> seq = []
 >>> c = coroutine(seq)
->>> c.next()
+>>> next(c)
 >>> print(seq)
 []
 >>> c.send(10)
@@ -1558,7 +1558,7 @@ Now check some throw() conditions:
 ...             print("caught ValueError (%s)" % (v))
 >>> import sys
 >>> g = f()
->>> g.next()
+>>> next(g)
 
 >>> g.throw(ValueError) # type only
 caught ValueError ()
@@ -1642,7 +1642,7 @@ Now let's try closing a generator:
 ...         print("exiting")
 
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> g.close()
 exiting
 >>> g.close()  # should be no-op now
@@ -1652,7 +1652,7 @@ exiting
 >>> def f(): yield      # an even simpler generator
 >>> f().close()         # close before opening
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> g.close()           # close normally
 
 And finalization:
@@ -1663,7 +1663,7 @@ And finalization:
 ...         print("exiting")
 
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> del g
 exiting
 
@@ -1675,7 +1675,7 @@ Now let's try some ill-behaved generators:
 ...     except GeneratorExit:
 ...         yield "foo!"
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> g.close()
 Traceback (most recent call last):
   ...
@@ -1688,7 +1688,7 @@ Our ill-behaved code should be invoked during GC:
 >>> import sys, StringIO
 >>> old, sys.stderr = sys.stderr, StringIO.StringIO()
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> del g
 >>> sys.stderr.getvalue().startswith(
 ...     "Exception RuntimeError: 'generator ignored GeneratorExit' in "
@@ -1704,7 +1704,7 @@ And errors thrown during closing should propagate:
 ...     except GeneratorExit:
 ...         raise TypeError("fie!")
 >>> g = f()
->>> g.next()
+>>> next(g)
 >>> g.close()
 Traceback (most recent call last):
   ...
@@ -1760,7 +1760,7 @@ would trigger if it starts being uncleanable again.
 ...     class gen:
 ...         def __iter__(self):
 ...             return self
-...         def next(self):
+...         def __next__(self):
 ...             return self.item
 ...     g = gen()
 ...     head, tail = itertools.tee(g)
@@ -1771,7 +1771,7 @@ would trigger if it starts being uncleanable again.
 Make sure to also test the involvement of the tee-internal teedataobject,
 which stores returned items.
 
->>> item = it.next()
+>>> item = next(it)
 
 
 

Lib/test/test_genexps.py

@@ -34,24 +34,24 @@ Test first class
 Test direct calls to next()
 
     >>> g = (i*i for i in range(3))
-    >>> g.next()
+    >>> next(g)
     0
-    >>> g.next()
+    >>> next(g)
     1
-    >>> g.next()
+    >>> next(g)
     4
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<pyshell#21>", line 1, in -toplevel-
-        g.next()
+        next(g)
     StopIteration
 
 Does it stay stopped?
 
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<pyshell#21>", line 1, in -toplevel-
-        g.next()
+        next(g)
     StopIteration
     >>> list(g)
     []
@@ -157,7 +157,7 @@ Generators always return to the most recent caller:
 
     >>> def creator():
     ...     r = yrange(5)
-    ...     print("creator", r.next())
+    ...     print("creator", next(r))
     ...     return r
     >>> def caller():
     ...     r = creator()
@@ -181,32 +181,32 @@ Generators can call other generators:
 
 Verify that a gen exp cannot be resumed while it is actively running:
 
-    >>> g = (me.next() for i in xrange(10))
+    >>> g = (next(me) for i in xrange(10))
     >>> me = g
-    >>> me.next()
+    >>> next(me)
     Traceback (most recent call last):
       File "<pyshell#30>", line 1, in -toplevel-
-        me.next()
+        next(me)
       File "<pyshell#28>", line 1, in <generator expression>
-        g = (me.next() for i in xrange(10))
+        g = (next(me) for i in xrange(10))
     ValueError: generator already executing
 
 Verify exception propagation
 
     >>> g = (10 // i for i in (5, 0, 2))
-    >>> g.next()
+    >>> next(g)
     2
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<pyshell#37>", line 1, in -toplevel-
-        g.next()
+        next(g)
       File "<pyshell#35>", line 1, in <generator expression>
         g = (10 // i for i in (5, 0, 2))
     ZeroDivisionError: integer division or modulo by zero
-    >>> g.next()
+    >>> next(g)
     Traceback (most recent call last):
       File "<pyshell#38>", line 1, in -toplevel-
-        g.next()
+        next(g)
     StopIteration
 
 Make sure that None is a valid return value
@@ -217,12 +217,12 @@ Make sure that None is a valid return value
 Check that generator attributes are present
 
     >>> g = (i*i for i in range(3))
-    >>> expected = set(['gi_frame', 'gi_running', 'next'])
+    >>> expected = set(['gi_frame', 'gi_running'])
     >>> set(attr for attr in dir(g) if not attr.startswith('__')) >= expected
     True
 
-    >>> print(g.next.__doc__)
-    x.next() -> the next value, or raise StopIteration
+    >>> print(g.__next__.__doc__)
+    x.__next__() <==> next(x)
     >>> import types
     >>> isinstance(g, types.GeneratorType)
     True
@@ -238,7 +238,7 @@ Verify that the running flag is set properly
     >>> me = g
     >>> me.gi_running
     0
-    >>> me.next()
+    >>> next(me)
     1
     >>> me.gi_running
     0

Lib/test/test_grammar.py

@@ -785,9 +785,9 @@ class GrammarTests(unittest.TestCase):
     def testGenexps(self):
         # generator expression tests
         g = ([x for x in range(10)] for x in range(1))
-        self.assertEqual(g.next(), [x for x in range(10)])
+        self.assertEqual(next(g), [x for x in range(10)])
         try:
-            g.next()
+            next(g)
             self.fail('should produce StopIteration exception')
         except StopIteration:
             pass
@@ -795,7 +795,7 @@ class GrammarTests(unittest.TestCase):
         a = 1
         try:
             g = (a for d in a)
-            g.next()
+            next(g)
             self.fail('should produce TypeError')
         except TypeError:
             pass

Lib/test/test_heapq.py

@@ -180,7 +180,7 @@ class I:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -200,14 +200,14 @@ class X:
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
         return v
 
 class N:
-    'Iterator missing next()'
+    'Iterator missing __next__()'
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
@@ -221,7 +221,7 @@ class E:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         3 // 0
 
 class S:
@@ -230,7 +230,7 @@ class S:
         pass
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         raise StopIteration
 
 from itertools import chain, imap

Lib/test/test_iter.py

@@ -22,7 +22,7 @@ class BasicIterClass:
     def __init__(self, n):
         self.n = n
         self.i = 0
-    def next(self):
+    def __next__(self):
         res = self.i
         if res >= self.n:
             raise StopIteration
@@ -53,7 +53,7 @@ class TestCase(unittest.TestCase):
         res = []
         while 1:
             try:
-                val = it.next()
+                val = next(it)
             except StopIteration:
                 break
             res.append(val)
@@ -342,7 +342,7 @@ class TestCase(unittest.TestCase):
                         self.i = 0
                     def __iter__(self):
                         return self
-                    def next(self):
+                    def __next__(self):
                         i = self.i
                         self.i = i + 1
                         if i < len(self.vals):
@@ -447,7 +447,7 @@ class TestCase(unittest.TestCase):
             def __iter__(self):
                 return self
 
-            def next(self):
+            def __next__(self):
                 i = self.i
                 self.i = i+1
                 return i
@@ -514,12 +514,12 @@ class TestCase(unittest.TestCase):
             def __iter__(self):
                 return self
 
-            def next(self):
+            def __next__(self):
                 i = self.i
                 self.i = i+1
                 if i == 2:
                     return unicode("fooled you!")
-                return self.it.next()
+                return next(self.it)
 
         f = open(TESTFN, "w")
         try:
@@ -682,7 +682,7 @@ class TestCase(unittest.TestCase):
                     self.finish = finish
                     self.i = self.start
 
-                def next(self):
+                def __next__(self):
                     if self.i >= self.finish:
                         raise StopIteration
                     result = str(self.i) + '\n'

Lib/test/test_iterlen.py

@@ -10,7 +10,7 @@ The desired invariant is:  len(it)==len(list(it)).
 A complication is that an iterable and iterator can be the same object. To
 maintain the invariant, an iterator needs to dynamically update its length.
 For instance, an iterable such as xrange(10) always reports its length as ten,
-but it=iter(xrange(10)) starts at ten, and then goes to nine after it.next().
+but it=iter(xrange(10)) starts at ten, and then goes to nine after next(it).
 Having this capability means that map() can ignore the distinction between
 map(func, iterable) and map(func, iter(iterable)).
 
@@ -67,9 +67,9 @@ class TestInvariantWithoutMutations(unittest.TestCase):
         it = self.it
         for i in reversed(xrange(1, n+1)):
             self.assertEqual(len(it), i)
-            it.next()
+            next(it)
         self.assertEqual(len(it), 0)
-        self.assertRaises(StopIteration, it.next)
+        self.assertRaises(StopIteration, next, it)
         self.assertEqual(len(it), 0)
 
 class TestTemporarilyImmutable(TestInvariantWithoutMutations):
@@ -80,10 +80,10 @@ class TestTemporarilyImmutable(TestInvariantWithoutMutations):
 
         it = self.it
         self.assertEqual(len(it), n)
-        it.next()
+        next(it)
         self.assertEqual(len(it), n-1)
         self.mutate()
-        self.assertRaises(RuntimeError, it.next)
+        self.assertRaises(RuntimeError, next, it)
         self.assertEqual(len(it), 0)
 
 ## ------- Concrete Type Tests -------
@@ -166,8 +166,8 @@ class TestList(TestInvariantWithoutMutations):
     def test_mutation(self):
         d = range(n)
         it = iter(d)
-        it.next()
-        it.next()
+        next(it)
+        next(it)
         self.assertEqual(len(it), n-2)
         d.append(n)
         self.assertEqual(len(it), n-1)  # grow with append
@@ -185,8 +185,8 @@ class TestListReversed(TestInvariantWithoutMutations):
     def test_mutation(self):
         d = range(n)
         it = reversed(d)
-        it.next()
-        it.next()
+        next(it)
+        next(it)
         self.assertEqual(len(it), n-2)
         d.append(n)
         self.assertEqual(len(it), n-2)  # ignore append
@@ -204,8 +204,8 @@ class TestSeqIter(TestInvariantWithoutMutations):
     def test_mutation(self):
         d = UserList(range(n))
         it = iter(d)
-        it.next()
-        it.next()
+        next(it)
+        next(it)
         self.assertEqual(len(it), n-2)
         d.append(n)
         self.assertEqual(len(it), n-1)  # grow with append
@@ -223,8 +223,8 @@ class TestSeqIterReversed(TestInvariantWithoutMutations):
     def test_mutation(self):
         d = UserList(range(n))
         it = reversed(d)
-        it.next()
-        it.next()
+        next(it)
+        next(it)
         self.assertEqual(len(it), n-2)
         d.append(n)
         self.assertEqual(len(it), n-2)  # ignore append

Lib/test/test_itertools.py

@@ -34,7 +34,7 @@ class StopNow:
     'Class emulating an empty iterable.'
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         raise StopIteration
 
 def take(n, seq):
@@ -58,12 +58,12 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(OverflowError, list, islice(count(sys.maxint-5), 10))
         c = count(3)
         self.assertEqual(repr(c), 'count(3)')
-        c.next()
+        next(c)
         self.assertEqual(repr(c), 'count(4)')
         c = count(-9)
         self.assertEqual(repr(c), 'count(-9)')
-        c.next()
-        self.assertEqual(c.next(), -8)
+        next(c)
+        self.assertEqual(next(c), -8)
 
     def test_cycle(self):
         self.assertEqual(take(10, cycle('abc')), list('abcabcabca'))
@@ -121,7 +121,7 @@ class TestBasicOps(unittest.TestCase):
         r = sorted([(len(list(g)) , k) for k, g in groupby(sorted(s))], reverse=True)[:3]
         self.assertEqual(r, [(5, 'a'), (2, 'r'), (2, 'b')])
 
-        # iter.next failure
+        # iter.__next__ failure
         class ExpectedError(Exception):
             pass
         def delayed_raise(n=0):
@@ -131,9 +131,9 @@ class TestBasicOps(unittest.TestCase):
         def gulp(iterable, keyp=None, func=list):
             return [func(g) for k, g in groupby(iterable, keyp)]
 
-        # iter.next failure on outer object
+        # iter.__next__ failure on outer object
         self.assertRaises(ExpectedError, gulp, delayed_raise(0))
-        # iter.next failure on inner object
+        # iter.__next__ failure on inner object
         self.assertRaises(ExpectedError, gulp, delayed_raise(1))
 
         # __cmp__ failure
@@ -169,7 +169,7 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(TypeError, ifilter, lambda x:x)
         self.assertRaises(TypeError, ifilter, lambda x:x, range(6), 7)
         self.assertRaises(TypeError, ifilter, isEven, 3)
-        self.assertRaises(TypeError, ifilter(range(6), range(6)).next)
+        self.assertRaises(TypeError, next, ifilter(range(6), range(6)))
 
     def test_ifilterfalse(self):
         self.assertEqual(list(ifilterfalse(isEven, range(6))), [1,3,5])
@@ -179,7 +179,7 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(TypeError, ifilterfalse, lambda x:x)
         self.assertRaises(TypeError, ifilterfalse, lambda x:x, range(6), 7)
         self.assertRaises(TypeError, ifilterfalse, isEven, 3)
-        self.assertRaises(TypeError, ifilterfalse(range(6), range(6)).next)
+        self.assertRaises(TypeError, next, ifilterfalse(range(6), range(6)))
 
     def test_izip(self):
         # XXX This is rather silly now that builtin zip() calls izip()...
@@ -276,9 +276,9 @@ class TestBasicOps(unittest.TestCase):
         self.assertEqual(list(imap(operator.pow, [])), [])
         self.assertRaises(TypeError, imap)
         self.assertRaises(TypeError, imap, operator.neg)
-        self.assertRaises(TypeError, imap(10, range(5)).next)
-        self.assertRaises(ValueError, imap(errfunc, [4], [5]).next)
-        self.assertRaises(TypeError, imap(onearg, [4], [5]).next)
+        self.assertRaises(TypeError, next, imap(10, range(5)))
+        self.assertRaises(ValueError, next, imap(errfunc, [4], [5]))
+        self.assertRaises(TypeError, next, imap(onearg, [4], [5]))
 
     def test_starmap(self):
         self.assertEqual(list(starmap(operator.pow, zip(range(3), range(1,7)))),
@@ -289,9 +289,9 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(TypeError, list, starmap(operator.pow, [[4,5]]))
         self.assertRaises(TypeError, starmap)
         self.assertRaises(TypeError, starmap, operator.pow, [(4,5)], 'extra')
-        self.assertRaises(TypeError, starmap(10, [(4,5)]).next)
-        self.assertRaises(ValueError, starmap(errfunc, [(4,5)]).next)
-        self.assertRaises(TypeError, starmap(onearg, [(4,5)]).next)
+        self.assertRaises(TypeError, next, starmap(10, [(4,5)]))
+        self.assertRaises(ValueError, next, starmap(errfunc, [(4,5)]))
+        self.assertRaises(TypeError, next, starmap(onearg, [(4,5)]))
 
     def test_islice(self):
         for args in [          # islice(args) should agree with range(args)
@@ -344,11 +344,11 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(TypeError, takewhile)
         self.assertRaises(TypeError, takewhile, operator.pow)
         self.assertRaises(TypeError, takewhile, operator.pow, [(4,5)], 'extra')
-        self.assertRaises(TypeError, takewhile(10, [(4,5)]).next)
-        self.assertRaises(ValueError, takewhile(errfunc, [(4,5)]).next)
+        self.assertRaises(TypeError, next, takewhile(10, [(4,5)]))
+        self.assertRaises(ValueError, next, takewhile(errfunc, [(4,5)]))
         t = takewhile(bool, [1, 1, 1, 0, 0, 0])
         self.assertEqual(list(t), [1, 1, 1])
-        self.assertRaises(StopIteration, t.next)
+        self.assertRaises(StopIteration, next, t)
 
     def test_dropwhile(self):
         data = [1, 3, 5, 20, 2, 4, 6, 8]
@@ -358,8 +358,8 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(TypeError, dropwhile)
         self.assertRaises(TypeError, dropwhile, operator.pow)
         self.assertRaises(TypeError, dropwhile, operator.pow, [(4,5)], 'extra')
-        self.assertRaises(TypeError, dropwhile(10, [(4,5)]).next)
-        self.assertRaises(ValueError, dropwhile(errfunc, [(4,5)]).next)
+        self.assertRaises(TypeError, next, dropwhile(10, [(4,5)]))
+        self.assertRaises(ValueError, next, dropwhile(errfunc, [(4,5)]))
 
     def test_tee(self):
         n = 200
@@ -380,13 +380,13 @@ class TestBasicOps(unittest.TestCase):
 
         a, b = tee(irange(n)) # test dealloc of leading iterator
         for i in xrange(100):
-            self.assertEqual(a.next(), i)
+            self.assertEqual(next(a), i)
         del a
         self.assertEqual(list(b), range(n))
 
         a, b = tee(irange(n)) # test dealloc of trailing iterator
         for i in xrange(100):
-            self.assertEqual(a.next(), i)
+            self.assertEqual(next(a), i)
         del b
         self.assertEqual(list(a), range(100, n))
 
@@ -396,7 +396,7 @@ class TestBasicOps(unittest.TestCase):
             lists = ([], [])
             its = tee(irange(n))
             for i in order:
-                value = its[i].next()
+                value = next(its[i])
                 lists[i].append(value)
             self.assertEqual(lists[0], range(n))
             self.assertEqual(lists[1], range(n))
@@ -415,9 +415,9 @@ class TestBasicOps(unittest.TestCase):
         # test long-lagged and multi-way split
         a, b, c = tee(xrange(2000), 3)
         for i in xrange(100):
-            self.assertEqual(a.next(), i)
+            self.assertEqual(next(a), i)
         self.assertEqual(list(b), range(2000))
-        self.assertEqual([c.next(), c.next()], range(2))
+        self.assertEqual([next(c), next(c)], range(2))
         self.assertEqual(list(a), range(100,2000))
         self.assertEqual(list(c), range(2,2000))
 
@@ -451,33 +451,33 @@ class TestBasicOps(unittest.TestCase):
         self.assertRaises(ReferenceError, getattr, p, '__class__')
 
     def test_StopIteration(self):
-        self.assertRaises(StopIteration, izip().next)
+        self.assertRaises(StopIteration, next, izip())
 
         for f in (chain, cycle, izip, groupby):
-            self.assertRaises(StopIteration, f([]).next)
-            self.assertRaises(StopIteration, f(StopNow()).next)
+            self.assertRaises(StopIteration, next, f([]))
+            self.assertRaises(StopIteration, next, f(StopNow()))
 
-        self.assertRaises(StopIteration, islice([], None).next)
-        self.assertRaises(StopIteration, islice(StopNow(), None).next)
+        self.assertRaises(StopIteration, next, islice([], None))
+        self.assertRaises(StopIteration, next, islice(StopNow(), None))
 
         p, q = tee([])
-        self.assertRaises(StopIteration, p.next)
-        self.assertRaises(StopIteration, q.next)
+        self.assertRaises(StopIteration, next, p)
+        self.assertRaises(StopIteration, next, q)
         p, q = tee(StopNow())
-        self.assertRaises(StopIteration, p.next)
-        self.assertRaises(StopIteration, q.next)
+        self.assertRaises(StopIteration, next, p)
+        self.assertRaises(StopIteration, next, q)
 
-        self.assertRaises(StopIteration, repeat(None, 0).next)
+        self.assertRaises(StopIteration, next, repeat(None, 0))
 
         for f in (ifilter, ifilterfalse, imap, takewhile, dropwhile, starmap):
-            self.assertRaises(StopIteration, f(lambda x:x, []).next)
-            self.assertRaises(StopIteration, f(lambda x:x, StopNow()).next)
+            self.assertRaises(StopIteration, next, f(lambda x:x, []))
+            self.assertRaises(StopIteration, next, f(lambda x:x, StopNow()))
 
 class TestGC(unittest.TestCase):
 
     def makecycle(self, iterator, container):
         container.append(iterator)
-        iterator.next()
+        next(iterator)
         del container, iterator
 
     def test_chain(self):
@@ -547,7 +547,7 @@ class I:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -567,14 +567,14 @@ class X:
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
         return v
 
 class N:
-    'Iterator missing next()'
+    'Iterator missing __next__()'
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
@@ -588,7 +588,7 @@ class E:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         3 // 0
 
 class S:
@@ -597,7 +597,7 @@ class S:
         pass
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         raise StopIteration
 
 def L(seqn):
@@ -748,13 +748,13 @@ class RegressionTests(unittest.TestCase):
             def g(value, first=[1]):
                 if first:
                     del first[:]
-                    f(z.next())
+                    f(next(z))
                 return value
             items = list(tuple2)
             items[1:1] = list(tuple1)
             gen = imap(g, items)
             z = izip(*[gen]*len(tuple1))
-            z.next()
+            next(z)
 
         def f(t):
             global T
@@ -930,7 +930,7 @@ Samuele
 ...     "s -> (s0,s1), (s1,s2), (s2, s3), ..."
 ...     a, b = tee(iterable)
 ...     try:
-...         b.next()
+...         next(b)
 ...     except StopIteration:
 ...         pass
 ...     return izip(a, b)

Lib/test/test_mailbox.py

@@ -1518,11 +1518,11 @@ class TestProxyFileBase(TestBase):
         # Iterate by line
         proxy.seek(0)
         iterator = iter(proxy)
-        self.assert_(iterator.next() == 'foo' + os.linesep)
-        self.assert_(iterator.next() == 'bar' + os.linesep)
-        self.assert_(iterator.next() == 'fred' + os.linesep)
-        self.assert_(iterator.next() == 'bob')
-        self.assertRaises(StopIteration, lambda: iterator.next())
+        self.assert_(next(iterator) == 'foo' + os.linesep)
+        self.assert_(next(iterator) == 'bar' + os.linesep)
+        self.assert_(next(iterator) == 'fred' + os.linesep)
+        self.assert_(next(iterator) == 'bob')
+        self.assertRaises(StopIteration, next, iterator)
 
     def _test_seek_and_tell(self, proxy):
         # Seek and use tell to check position

Lib/test/test_re.py

@@ -586,8 +586,8 @@ class ReTests(unittest.TestCase):
 
     def test_bug_581080(self):
         iter = re.finditer(r"\s", "a b")
-        self.assertEqual(iter.next().span(), (1,2))
-        self.assertRaises(StopIteration, iter.next)
+        self.assertEqual(next(iter).span(), (1,2))
+        self.assertRaises(StopIteration, next, iter)
 
         scanner = re.compile(r"\s").scanner("a b")
         self.assertEqual(scanner.search().span(), (1, 2))
@@ -595,9 +595,9 @@ class ReTests(unittest.TestCase):
 
     def test_bug_817234(self):
         iter = re.finditer(r".*", "asdf")
-        self.assertEqual(iter.next().span(), (0, 4))
-        self.assertEqual(iter.next().span(), (4, 4))
-        self.assertRaises(StopIteration, iter.next)
+        self.assertEqual(next(iter).span(), (0, 4))
+        self.assertEqual(next(iter).span(), (4, 4))
+        self.assertRaises(StopIteration, next, iter)
 
 
 def run_re_tests():

Lib/test/test_set.py

@@ -1382,7 +1382,7 @@ class I:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
@@ -1402,14 +1402,14 @@ class X:
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
-    def next(self):
+    def __next__(self):
         if self.i >= len(self.seqn): raise StopIteration
         v = self.seqn[self.i]
         self.i += 1
         return v
 
 class N:
-    'Iterator missing next()'
+    'Iterator missing __next__()'
     def __init__(self, seqn):
         self.seqn = seqn
         self.i = 0
@@ -1423,7 +1423,7 @@ class E:
         self.i = 0
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         3 // 0
 
 class S:
@@ -1432,7 +1432,7 @@ class S:
         pass
     def __iter__(self):
         return self
-    def next(self):
+    def __next__(self):
         raise StopIteration
 
 from itertools import chain, imap

Lib/test/test_str.py

@@ -22,10 +22,10 @@ class StrTest(
     def test_iterators(self):
         # Make sure str objects have an __iter__ method
         it = "abc".__iter__()
-        self.assertEqual(it.next(), "a")
-        self.assertEqual(it.next(), "b")
-        self.assertEqual(it.next(), "c")
-        self.assertRaises(StopIteration, it.next)
+        self.assertEqual(next(it), "a")
+        self.assertEqual(next(it), "b")
+        self.assertEqual(next(it), "c")
+        self.assertRaises(StopIteration, next, it)
 
     def test_conversion(self):
         # Make sure __str__() behaves properly

Lib/test/test_tempfile.py

@@ -102,7 +102,7 @@ class test__RandomNameSequence(TC):
 
     def test_get_six_char_str(self):
         # _RandomNameSequence returns a six-character string
-        s = self.r.next()
+        s = next(self.r)
         self.nameCheck(s, '', '', '')
 
     def test_many(self):
@@ -111,7 +111,7 @@ class test__RandomNameSequence(TC):
         dict = {}
         r = self.r
         for i in xrange(TEST_FILES):
-            s = r.next()
+            s = next(r)
             self.nameCheck(s, '', '', '')
             self.failIf(s in dict)
             dict[s] = 1

Lib/test/test_tokenize.py

@@ -103,7 +103,7 @@ def test_roundtrip(f):
 
     t1 = [tok[:2] for tok in fulltok]
     newtext = untokenize(t1)
-    readline = iter(newtext.splitlines(1)).next
+    readline = iter(newtext.splitlines(1)).__next__
     t2 = [tok[:2] for tok in generate_tokens(readline)]
     if t1 != t2:
         raise TestFailed("untokenize() roundtrip failed for %r" % f)
@@ -224,7 +224,7 @@ def test_rarrow():
     This function exists solely to test the tokenization of the RARROW
     operator.
 
-    >>> tokenize(iter(['->']).next)   #doctest: +NORMALIZE_WHITESPACE
+    >>> tokenize(iter(['->']).__next__)   #doctest: +NORMALIZE_WHITESPACE
     1,0-1,2:\tOP\t'->'
     2,0-2,0:\tENDMARKER\t''
     """

Lib/test/test_unicode.py

@@ -99,10 +99,10 @@ class UnicodeTest(
     def test_iterators(self):
         # Make sure unicode objects have an __iter__ method
         it = u"\u1111\u2222\u3333".__iter__()
-        self.assertEqual(it.next(), u"\u1111")
-        self.assertEqual(it.next(), u"\u2222")
-        self.assertEqual(it.next(), u"\u3333")
-        self.assertRaises(StopIteration, it.next)
+        self.assertEqual(next(it), u"\u1111")
+        self.assertEqual(next(it), u"\u2222")
+        self.assertEqual(next(it), u"\u3333")
+        self.assertRaises(StopIteration, next, it)
 
     def test_count(self):
         string_tests.CommonTest.test_count(self)

Lib/test/test_userlist.py

@@ -51,7 +51,7 @@ class UserListTest(list_tests.CommonTest):
         class T(self.type2test):
             def __getitem__(self, key):
                 return str(key) + '!!!'
-        self.assertEqual(iter(T((1,2))).next(), "0!!!")
+        self.assertEqual(next(iter(T((1,2)))), "0!!!")
 
 def test_main():
     test_support.run_unittest(UserListTest)

Lib/test/test_wsgiref.py

@@ -108,13 +108,13 @@ def compare_generic_iter(make_it,match):
         it = make_it()
         if not iter(it) is it: raise AssertionError
         for item in match:
-            if not it.next()==item: raise AssertionError
+            if not next(it) == item: raise AssertionError
         try:
-            it.next()
+            next(it)
         except StopIteration:
             pass
         else:
-            raise AssertionError("Too many items from .next()",it)
+            raise AssertionError("Too many items from .__next__()", it)
 
 
 

Lib/tokenize.py

@@ -228,7 +228,7 @@ def untokenize(iterable):
         # Output text will tokenize the back to the input
         t1 = [tok[:2] for tok in generate_tokens(f.readline)]
         newcode = untokenize(t1)
-        readline = iter(newcode.splitlines(1)).next
+        readline = iter(newcode.splitlines(1)).__next__
         t2 = [tok[:2] for tokin generate_tokens(readline)]
         assert t1 == t2
     """
@@ -242,7 +242,7 @@ def generate_tokens(readline):
     readline() method of built-in file objects. Each call to the function
     should return one line of input as a string.  Alternately, readline
     can be a callable function terminating with StopIteration:
-        readline = open(myfile).next    # Example of alternate readline
+        readline = open(myfile).__next__    # Example of alternate readline
 
     The generator produces 5-tuples with these members: the token type; the
     token string; a 2-tuple (srow, scol) of ints specifying the row and

Lib/types.py

@@ -7,7 +7,7 @@ import sys
 # Iterators in Python aren't a matter of type but of protocol.  A large
 # and changing number of builtin types implement *some* flavor of
 # iterator.  Don't check the type!  Use hasattr to check for both
-# "__iter__" and "next" attributes instead.
+# "__iter__" and "__next__" attributes instead.
 
 NoneType = type(None)
 TypeType = type

Lib/urllib.py

@@ -902,8 +902,8 @@ class addbase:
             self.fileno = lambda: None
         if hasattr(self.fp, "__iter__"):
             self.__iter__ = self.fp.__iter__
-            if hasattr(self.fp, "next"):
-                self.next = self.fp.next
+            if hasattr(self.fp, "__next__"):
+                self.__next__ = self.fp.__next__
 
     def __repr__(self):
         return '<%s at %r whose fp = %r>' % (self.__class__.__name__,

Lib/wsgiref/util.py

@@ -26,7 +26,7 @@ class FileWrapper:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         data = self.filelike.read(self.blksize)
         if data:
             return data

Lib/wsgiref/validate.py

@@ -98,7 +98,7 @@ Some of the things this checks:
   - That it is not a string (it should be a list of a single string; a
     string will work, but perform horribly).
 
-  - That .next() returns a string
+  - That .__next__() returns a string
 
   - That the iterator is not iterated over until start_response has
     been called (that can signal either a server or application
@@ -265,10 +265,10 @@ class IteratorWrapper:
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         assert_(not self.closed,
             "Iterator read after closed")
-        v = self.iterator.next()
+        v = next(self.iterator)
         if self.check_start_response is not None:
             assert_(self.check_start_response,
                 "The application returns and we started iterating over its body, but start_response has not yet been called")

Lib/xml/dom/pulldom.py

@@ -228,7 +228,7 @@ class DOMEventStream:
             return rc
         raise IndexError
 
-    def next(self):
+    def __next__(self):
         rc = self.getEvent()
         if rc:
             return rc

Lib/xml/etree/ElementTree.py

@@ -893,7 +893,7 @@ class iterparse:
                     append((event, None))
                 parser.EndNamespaceDeclHandler = handler
 
-    def next(self):
+    def __next__(self):
         while 1:
             try:
                 item = self._events[self._index]
@@ -923,7 +923,7 @@ class iterparse:
             return self
     except NameError:
         def __getitem__(self, index):
-            return self.next()
+            return self.__next__()
 
 ##
 # Parses an XML document from a string constant.  This function can

Misc/Vim/vim_syntax.py

@@ -139,7 +139,7 @@ def fill_stmt(iterable, fill_len):
             overflow = None
         while total_len < fill_len:
             try:
-                new_item = it.next()
+                new_item = next(it)
                 buffer_.append(new_item)
                 total_len += len(new_item) + 1
             except StopIteration:
@@ -188,7 +188,7 @@ def main(file_path):
                                             FILL - len(prefix) - len(indent))
                         try:
                             while True:
-                                print>>FILE, indent + prefix + stmt_iter.next()
+                                print>>FILE, indent + prefix + next(stmt_iter)
                         except StopIteration:
                             print>>FILE, ''
                     else:

Misc/cheatsheet

@@ -721,7 +721,7 @@ File Exceptions
     return [result] -- Exits from function (or method) and returns result (use a tuple to
                        return more than one value). If no result given, then returns None.
     yield result    -- Freezes the execution frame of a generator and returns the result
-                       to the iterator's .next() method.  Upon the next call to next(),
+                       to the iterator's .__next__() method.  Upon the next call to __next__(),
                        resumes execution at the frozen point with all of the local variables
                        still intact.
 
@@ -1058,7 +1058,7 @@ Exception>
     SystemExit
          On 'sys.exit()'
     StopIteration
-         Signal the end from iterator.next()
+         Signal the end from iterator.__next__()
     StandardError
                  Base class for all built-in exceptions; derived from Exception
     root class.

Modules/itertoolsmodule.c

@@ -1701,7 +1701,7 @@ chain_next(chainobject *lz)
 PyDoc_STRVAR(chain_doc,
 "chain(*iterables) --> chain object\n\
 \n\
-Return a chain object whose .next() method returns elements from the\n\
+Return a chain object whose .__next__() method returns elements from the\n\
 first iterable until it is exhausted, then elements from the next\n\
 iterable, until all of the iterables are exhausted.");
 
@@ -2090,7 +2090,7 @@ count_repr(countobject *lz)
 PyDoc_STRVAR(count_doc,
 "count([firstval]) --> count object\n\
 \n\
-Return a count object whose .next() method returns consecutive\n\
+Return a count object whose .__next__() method returns consecutive\n\
 integers starting from zero or, if specified, from firstval.");
 
 static PyTypeObject count_type = {
@@ -2272,8 +2272,8 @@ izip_next(izipobject *lz)
 PyDoc_STRVAR(izip_doc,
 "izip(iter1 [,iter2 [...]]) --> izip object\n\
 \n\
-Return a izip object whose .next() method returns a tuple where\n\
-the i-th element comes from the i-th iterable argument.  The .next()\n\
+Return a izip object whose .__next__() method returns a tuple where\n\
+the i-th element comes from the i-th iterable argument.  The .__next__()\n\
 method continues until the shortest iterable in the argument sequence\n\
 is exhausted and then it raises StopIteration.  Works like the zip()\n\
 function but consumes less memory by returning an iterator instead of\n\
@@ -2648,8 +2648,8 @@ izip_longest_next(iziplongestobject *lz)
 PyDoc_STRVAR(izip_longest_doc,
 "izip_longest(iter1 [,iter2 [...]], [fillvalue=None]) --> izip_longest object\n\
 \n\
-Return an izip_longest object whose .next() method returns a tuple where\n\
-the i-th element comes from the i-th iterable argument.  The .next()\n\
+Return an izip_longest object whose .__next__() method returns a tuple where\n\
+the i-th element comes from the i-th iterable argument.  The .__next__()\n\
 method continues until the longest iterable in the argument sequence\n\
 is exhausted and then it raises StopIteration.  When the shorter iterables\n\
 are exhausted, the fillvalue is substituted in their place.  The fillvalue\n\

Objects/exceptions.c

@@ -369,7 +369,7 @@ SimpleExtendsException(PyExc_StandardError, TypeError,
  *    StopIteration extends Exception
  */
 SimpleExtendsException(PyExc_Exception, StopIteration,
-                       "Signal the end from iterator.next().");
+                       "Signal the end from iterator.__next__().");
 
 
 /*

Objects/typeobject.c

@@ -4636,7 +4636,7 @@ static PyObject *
 slot_tp_iternext(PyObject *self)
 {
 	static PyObject *next_str;
-	return call_method(self, "next", &next_str, "()");
+	return call_method(self, "__next__", &next_str, "()");
 }
 
 static PyObject *
@@ -5031,8 +5031,8 @@ static slotdef slotdefs[] = {
 	       "x.__ge__(y) <==> x>=y"),
 	TPSLOT("__iter__", tp_iter, slot_tp_iter, wrap_unaryfunc,
 	       "x.__iter__() <==> iter(x)"),
-	TPSLOT("next", tp_iternext, slot_tp_iternext, wrap_next,
-	       "x.next() -> the next value, or raise StopIteration"),
+	TPSLOT("__next__", tp_iternext, slot_tp_iternext, wrap_next,
+	       "x.__next__() <==> next(x)"),
 	TPSLOT("__get__", tp_descr_get, slot_tp_descr_get, wrap_descr_get,
 	       "descr.__get__(obj[, type]) -> value"),
 	TPSLOT("__set__", tp_descr_set, slot_tp_descr_set, wrap_descr_set,

Python/bltinmodule.c

@@ -1136,6 +1136,46 @@ sequences have the same length.  If the function is None, return a list of\n\
 the items of the sequence (or a list of tuples if more than one sequence).");
 
 
+static PyObject *
+builtin_next(PyObject *self, PyObject *args)
+{
+	PyObject *it, *res;
+	PyObject *def = NULL;
+
+	if (!PyArg_UnpackTuple(args, "next", 1, 2, &it, &def))
+		return NULL;
+	if (!PyIter_Check(it)) {
+		PyErr_Format(PyExc_TypeError,
+			"%.200s object is not an iterator", it->ob_type->tp_name);
+		return NULL;
+	}
+	
+	res = (*it->ob_type->tp_iternext)(it);
+	if (res == NULL) {
+		if (def) {
+			if (PyErr_Occurred() &&
+			    !PyErr_ExceptionMatches(PyExc_StopIteration))
+				return NULL;
+			PyErr_Clear();
+			Py_INCREF(def);
+			return def;
+		} else if (PyErr_Occurred()) {
+			return NULL;
+		} else {
+			PyErr_SetNone(PyExc_StopIteration);
+			return NULL;
+		}
+	}
+	return res;
+}
+
+PyDoc_STRVAR(next_doc,
+"next(iterator[, default])\n\
+\n\
+Return the next item from the iterator. If default is given and the iterator\n\
+is exhausted, it is returned instead of raising StopIteration.");
+
+
 static PyObject *
 builtin_setattr(PyObject *self, PyObject *args)
 {
@@ -2252,6 +2292,7 @@ static PyMethodDef builtin_methods[] = {
  	{"map",		builtin_map,        METH_VARARGS, map_doc},
  	{"max",		(PyCFunction)builtin_max,        METH_VARARGS | METH_KEYWORDS, max_doc},
  	{"min",		(PyCFunction)builtin_min,        METH_VARARGS | METH_KEYWORDS, min_doc},
+	{"next",	(PyCFunction)builtin_next,       METH_VARARGS, next_doc},
  	{"oct",		builtin_oct,        METH_O, oct_doc},
  	{"open",	(PyCFunction)builtin_open,       METH_VARARGS | METH_KEYWORDS, open_doc},
  	{"ord",		builtin_ord,        METH_O, ord_doc},

Tools/scripts/cleanfuture.py

@@ -162,7 +162,7 @@ class FutureFinder:
         OP = tokenize.OP
 
         changed = self.changed
-        get = tokenize.generate_tokens(self.getline).next
+        get = tokenize.generate_tokens(self.getline).__next__
         type, token, (srow, scol), (erow, ecol), line = get()
 
         # Chew up initial comments and blank lines (if any).