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1321 lines
60 KiB
TeX
1321 lines
60 KiB
TeX
\section{Built-in Functions \label{built-in-funcs}}
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The Python interpreter has a number of functions built into it that
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are always available. They are listed here in alphabetical order.
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\setindexsubitem{(built-in function)}
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\begin{funcdesc}{__import__}{name\optional{, globals\optional{, locals\optional{, fromlist\optional{, level}}}}}
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This function is invoked by the \keyword{import}\stindex{import}
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statement. It mainly exists so that you can replace it with another
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function that has a compatible interface, in order to change the
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semantics of the \keyword{import} statement. For examples of why
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and how you would do this, see the standard library modules
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\module{ihooks}\refstmodindex{ihooks} and
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\refmodule{rexec}\refstmodindex{rexec}. See also the built-in
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module \refmodule{imp}\refbimodindex{imp}, which defines some useful
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operations out of which you can build your own
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\function{__import__()} function.
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For example, the statement \samp{import spam} results in the
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following call: \code{__import__('spam',} \code{globals(),}
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\code{locals(), [], -1)}; the statement \samp{from spam.ham import eggs}
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results in \samp{__import__('spam.ham', globals(), locals(),
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['eggs'], -1)}. Note that even though \code{locals()} and
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\code{['eggs']} are passed in as arguments, the
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\function{__import__()} function does not set the local variable
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named \code{eggs}; this is done by subsequent code that is generated
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for the import statement. (In fact, the standard implementation
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does not use its \var{locals} argument at all, and uses its
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\var{globals} only to determine the package context of the
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\keyword{import} statement.)
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When the \var{name} variable is of the form \code{package.module},
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normally, the top-level package (the name up till the first dot) is
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returned, \emph{not} the module named by \var{name}. However, when
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a non-empty \var{fromlist} argument is given, the module named by
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\var{name} is returned. This is done for compatibility with the
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bytecode generated for the different kinds of import statement; when
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using \samp{import spam.ham.eggs}, the top-level package \module{spam}
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must be placed in the importing namespace, but when using \samp{from
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spam.ham import eggs}, the \code{spam.ham} subpackage must be used
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to find the \code{eggs} variable. As a workaround for this
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behavior, use \function{getattr()} to extract the desired
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components. For example, you could define the following helper:
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\begin{verbatim}
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def my_import(name):
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mod = __import__(name)
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components = name.split('.')
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for comp in components[1:]:
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mod = getattr(mod, comp)
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return mod
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\end{verbatim}
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\var{level} specifies whether to use absolute or relative imports.
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The default is \code{-1} which indicates both absolute and relative
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imports will be attempted. \code{0} means only perform absolute imports.
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Positive values for \var{level} indicate the number of parent directories
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to search relative to the directory of the module calling
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\function{__import__}.
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\versionchanged[The level parameter was added]{2.5}
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\versionchanged[Keyword support for parameters was added]{2.5}
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\end{funcdesc}
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\begin{funcdesc}{abs}{x}
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Return the absolute value of a number. The argument may be a plain
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or long integer or a floating point number. If the argument is a
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complex number, its magnitude is returned.
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\end{funcdesc}
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\begin{funcdesc}{all}{iterable}
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Return True if all elements of the \var{iterable} are true.
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Equivalent to:
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\begin{verbatim}
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def all(iterable):
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for element in iterable:
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if not element:
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return False
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return True
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\end{verbatim}
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\versionadded{2.5}
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\end{funcdesc}
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\begin{funcdesc}{any}{iterable}
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Return True if any element of the \var{iterable} is true.
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Equivalent to:
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\begin{verbatim}
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def any(iterable):
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for element in iterable:
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if element:
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return True
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return False
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\end{verbatim}
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\versionadded{2.5}
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\end{funcdesc}
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\begin{funcdesc}{basestring}{}
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This abstract type is the superclass for \class{str} and \class{unicode}.
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It cannot be called or instantiated, but it can be used to test whether
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an object is an instance of \class{str} or \class{unicode}.
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\code{isinstance(obj, basestring)} is equivalent to
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\code{isinstance(obj, (str, unicode))}.
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\versionadded{2.3}
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\end{funcdesc}
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\begin{funcdesc}{bool}{\optional{x}}
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Convert a value to a Boolean, using the standard truth testing
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procedure. If \var{x} is false or omitted, this returns
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\constant{False}; otherwise it returns \constant{True}.
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\class{bool} is also a class, which is a subclass of \class{int}.
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Class \class{bool} cannot be subclassed further. Its only instances
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are \constant{False} and \constant{True}.
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\indexii{Boolean}{type}
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\versionadded{2.2.1}
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\versionchanged[If no argument is given, this function returns
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\constant{False}]{2.3}
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\end{funcdesc}
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\begin{funcdesc}{callable}{object}
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Return true if the \var{object} argument appears callable, false if
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not. If this returns true, it is still possible that a call fails,
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but if it is false, calling \var{object} will never succeed. Note
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that classes are callable (calling a class returns a new instance);
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class instances are callable if they have a \method{__call__()}
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method.
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\end{funcdesc}
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\begin{funcdesc}{chr}{i}
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Return a string of one character whose \ASCII{} code is the integer
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\var{i}. For example, \code{chr(97)} returns the string \code{'a'}.
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This is the inverse of \function{ord()}. The argument must be in
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the range [0..255], inclusive; \exception{ValueError} will be raised
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if \var{i} is outside that range.
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\end{funcdesc}
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\begin{funcdesc}{classmethod}{function}
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Return a class method for \var{function}.
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A class method receives the class as implicit first argument,
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just like an instance method receives the instance.
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To declare a class method, use this idiom:
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\begin{verbatim}
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class C:
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@classmethod
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def f(cls, arg1, arg2, ...): ...
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\end{verbatim}
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The \code{@classmethod} form is a function decorator -- see the description
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of function definitions in chapter 7 of the
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\citetitle[../ref/ref.html]{Python Reference Manual} for details.
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It can be called either on the class (such as \code{C.f()}) or on an
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instance (such as \code{C().f()}). The instance is ignored except for
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its class.
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If a class method is called for a derived class, the derived class
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object is passed as the implied first argument.
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Class methods are different than \Cpp{} or Java static methods.
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If you want those, see \function{staticmethod()} in this section.
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For more information on class methods, consult the documentation on the
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standard type hierarchy in chapter 3 of the
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\citetitle[../ref/types.html]{Python Reference Manual} (at the bottom).
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\versionadded{2.2}
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\versionchanged[Function decorator syntax added]{2.4}
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\end{funcdesc}
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\begin{funcdesc}{cmp}{x, y}
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Compare the two objects \var{x} and \var{y} and return an integer
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according to the outcome. The return value is negative if \code{\var{x}
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< \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if
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\code{\var{x} > \var{y}}.
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\end{funcdesc}
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\begin{funcdesc}{compile}{string, filename, kind\optional{,
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flags\optional{, dont_inherit}}}
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Compile the \var{string} into a code object. Code objects can be
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executed by an \keyword{exec} statement or evaluated by a call to
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\function{eval()}. The \var{filename} argument should
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give the file from which the code was read; pass some recognizable value
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if it wasn't read from a file (\code{'<string>'} is commonly used).
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The \var{kind} argument specifies what kind of code must be
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compiled; it can be \code{'exec'} if \var{string} consists of a
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sequence of statements, \code{'eval'} if it consists of a single
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expression, or \code{'single'} if it consists of a single
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interactive statement (in the latter case, expression statements
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that evaluate to something else than \code{None} will be printed).
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When compiling multi-line statements, two caveats apply: line
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endings must be represented by a single newline character
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(\code{'\e n'}), and the input must be terminated by at least one
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newline character. If line endings are represented by
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\code{'\e r\e n'}, use the string \method{replace()} method to
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change them into \code{'\e n'}.
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The optional arguments \var{flags} and \var{dont_inherit}
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(which are new in Python 2.2) control which future statements (see
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\pep{236}) affect the compilation of \var{string}. If neither is
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present (or both are zero) the code is compiled with those future
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statements that are in effect in the code that is calling compile.
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If the \var{flags} argument is given and \var{dont_inherit} is not
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(or is zero) then the future statements specified by the \var{flags}
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argument are used in addition to those that would be used anyway.
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If \var{dont_inherit} is a non-zero integer then the \var{flags}
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argument is it -- the future statements in effect around the call to
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compile are ignored.
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Future statements are specified by bits which can be bitwise or-ed
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together to specify multiple statements. The bitfield required to
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specify a given feature can be found as the \member{compiler_flag}
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attribute on the \class{_Feature} instance in the
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\module{__future__} module.
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\end{funcdesc}
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\begin{funcdesc}{complex}{\optional{real\optional{, imag}}}
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Create a complex number with the value \var{real} + \var{imag}*j or
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convert a string or number to a complex number. If the first
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parameter is a string, it will be interpreted as a complex number
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and the function must be called without a second parameter. The
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second parameter can never be a string.
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Each argument may be any numeric type (including complex).
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If \var{imag} is omitted, it defaults to zero and the function
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serves as a numeric conversion function like \function{int()},
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\function{long()} and \function{float()}. If both arguments
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are omitted, returns \code{0j}.
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\end{funcdesc}
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\begin{funcdesc}{delattr}{object, name}
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This is a relative of \function{setattr()}. The arguments are an
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object and a string. The string must be the name
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of one of the object's attributes. The function deletes
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the named attribute, provided the object allows it. For example,
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\code{delattr(\var{x}, '\var{foobar}')} is equivalent to
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\code{del \var{x}.\var{foobar}}.
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\end{funcdesc}
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\begin{funcdesc}{dict}{\optional{arg}}
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Return a new dictionary initialized from an optional positional
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argument or from a set of keyword arguments.
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If no arguments are given, return a new empty dictionary.
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If the positional argument \var{arg} is a mapping object, return a dictionary
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mapping the same keys to the same values as does the mapping object.
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Otherwise the positional argument must be a sequence, a container that
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supports iteration, or an iterator object. The elements of the argument
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must each also be of one of those kinds, and each must in turn contain
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exactly two objects. The first is used as a key in the new dictionary,
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and the second as the key's value. If a given key is seen more than
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once, the last value associated with it is retained in the new
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dictionary.
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If keyword arguments are given, the keywords themselves with their
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associated values are added as items to the dictionary. If a key
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is specified both in the positional argument and as a keyword argument,
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the value associated with the keyword is retained in the dictionary.
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For example, these all return a dictionary equal to
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\code{\{"one": 2, "two": 3\}}:
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\begin{itemize}
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\item \code{dict(\{'one': 2, 'two': 3\})}
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\item \code{dict(\{'one': 2, 'two': 3\}.items())}
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\item \code{dict(\{'one': 2, 'two': 3\}.iteritems())}
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\item \code{dict(zip(('one', 'two'), (2, 3)))}
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\item \code{dict([['two', 3], ['one', 2]])}
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\item \code{dict(one=2, two=3)}
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\item \code{dict([(['one', 'two'][i-2], i) for i in (2, 3)])}
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\end{itemize}
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\versionadded{2.2}
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\versionchanged[Support for building a dictionary from keyword
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arguments added]{2.3}
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\end{funcdesc}
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\begin{funcdesc}{dir}{\optional{object}}
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Without arguments, return the list of names in the current local
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symbol table. With an argument, attempts to return a list of valid
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attributes for that object. This information is gleaned from the
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object's \member{__dict__} attribute, if defined, and from the class
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or type object. The list is not necessarily complete.
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If the object is a module object, the list contains the names of the
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module's attributes.
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If the object is a type or class object,
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the list contains the names of its attributes,
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and recursively of the attributes of its bases.
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Otherwise, the list contains the object's attributes' names,
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the names of its class's attributes,
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and recursively of the attributes of its class's base classes.
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The resulting list is sorted alphabetically.
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For example:
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\begin{verbatim}
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>>> import struct
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>>> dir()
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['__builtins__', '__doc__', '__name__', 'struct']
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>>> dir(struct)
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['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack']
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\end{verbatim}
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\note{Because \function{dir()} is supplied primarily as a convenience
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for use at an interactive prompt,
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it tries to supply an interesting set of names more than it tries to
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supply a rigorously or consistently defined set of names,
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and its detailed behavior may change across releases.}
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\end{funcdesc}
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\begin{funcdesc}{divmod}{a, b}
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Take two (non complex) numbers as arguments and return a pair of numbers
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consisting of their quotient and remainder when using long division. With
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mixed operand types, the rules for binary arithmetic operators apply. For
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plain and long integers, the result is the same as
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\code{(\var{a} // \var{b}, \var{a} \%{} \var{b})}.
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For floating point numbers the result is \code{(\var{q}, \var{a} \%{}
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\var{b})}, where \var{q} is usually \code{math.floor(\var{a} /
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\var{b})} but may be 1 less than that. In any case \code{\var{q} *
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\var{b} + \var{a} \%{} \var{b}} is very close to \var{a}, if
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\code{\var{a} \%{} \var{b}} is non-zero it has the same sign as
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\var{b}, and \code{0 <= abs(\var{a} \%{} \var{b}) < abs(\var{b})}.
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\versionchanged[Using \function{divmod()} with complex numbers is
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deprecated]{2.3}
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\end{funcdesc}
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\begin{funcdesc}{enumerate}{iterable}
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Return an enumerate object. \var{iterable} must be a sequence, an
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iterator, or some other object which supports iteration. The
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\method{next()} method of the iterator returned by
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\function{enumerate()} returns a tuple containing a count (from
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zero) and the corresponding value obtained from iterating over
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\var{iterable}. \function{enumerate()} is useful for obtaining an
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indexed series: \code{(0, seq[0])}, \code{(1, seq[1])}, \code{(2,
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seq[2])}, \ldots.
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\versionadded{2.3}
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\end{funcdesc}
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\begin{funcdesc}{eval}{expression\optional{, globals\optional{, locals}}}
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The arguments are a string and optional globals and locals. If provided,
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\var{globals} must be a dictionary. If provided, \var{locals} can be
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any mapping object. \versionchanged[formerly \var{locals} was required
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to be a dictionary]{2.4}
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The \var{expression} argument is parsed and evaluated as a Python
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expression (technically speaking, a condition list) using the
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\var{globals} and \var{locals} dictionaries as global and local name
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space. If the \var{globals} dictionary is present and lacks
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'__builtins__', the current globals are copied into \var{globals} before
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\var{expression} is parsed. This means that \var{expression}
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normally has full access to the standard
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\refmodule[builtin]{__builtin__} module and restricted environments
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are propagated. If the \var{locals} dictionary is omitted it defaults to
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the \var{globals} dictionary. If both dictionaries are omitted, the
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expression is executed in the environment where \keyword{eval} is
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called. The return value is the result of the evaluated expression.
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Syntax errors are reported as exceptions. Example:
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\begin{verbatim}
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>>> x = 1
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>>> print eval('x+1')
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2
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\end{verbatim}
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This function can also be used to execute arbitrary code objects
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(such as those created by \function{compile()}). In this case pass
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a code object instead of a string. The code object must have been
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compiled passing \code{'eval'} as the \var{kind} argument.
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Hints: dynamic execution of statements is supported by the
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\keyword{exec} statement. Execution of statements from a file is
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supported by the \function{execfile()} function. The
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\function{globals()} and \function{locals()} functions returns the
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current global and local dictionary, respectively, which may be
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useful to pass around for use by \function{eval()} or
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\function{execfile()}.
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\end{funcdesc}
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\begin{funcdesc}{execfile}{filename\optional{, globals\optional{, locals}}}
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This function is similar to the
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\keyword{exec} statement, but parses a file instead of a string. It
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is different from the \keyword{import} statement in that it does not
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use the module administration --- it reads the file unconditionally
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and does not create a new module.\footnote{It is used relatively
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rarely so does not warrant being made into a statement.}
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The arguments are a file name and two optional dictionaries. The file is
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parsed and evaluated as a sequence of Python statements (similarly to a
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module) using the \var{globals} and \var{locals} dictionaries as global and
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local namespace. If provided, \var{locals} can be any mapping object.
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\versionchanged[formerly \var{locals} was required to be a dictionary]{2.4}
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If the \var{locals} dictionary is omitted it defaults to the \var{globals}
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dictionary. If both dictionaries are omitted, the expression is executed in
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the environment where \function{execfile()} is called. The return value is
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\code{None}.
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\warning{The default \var{locals} act as described for function
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\function{locals()} below: modifications to the default \var{locals}
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dictionary should not be attempted. Pass an explicit \var{locals}
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dictionary if you need to see effects of the code on \var{locals} after
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function \function{execfile()} returns. \function{execfile()} cannot
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be used reliably to modify a function's locals.}
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\end{funcdesc}
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\begin{funcdesc}{file}{filename\optional{, mode\optional{, bufsize}}}
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Constructor function for the \class{file} type, described further
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in section~\ref{bltin-file-objects}, ``\ulink{File
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Objects}{bltin-file-objects.html}''. The constructor's arguments
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are the same as those of the \function{open()} built-in function
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described below.
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When opening a file, it's preferable to use \function{open()} instead of
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invoking this constructor directly. \class{file} is more suited to
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type testing (for example, writing \samp{isinstance(f, file)}).
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\versionadded{2.2}
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\end{funcdesc}
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\begin{funcdesc}{filter}{function, iterable}
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Construct a list from those elements of \var{iterable} for which
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\var{function} returns true. \var{iterable} may be either a sequence, a
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container which supports iteration, or an iterator, If \var{iterable}
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is a string or a tuple, the result
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|
also has that type; otherwise it is always a list. If \var{function} is
|
|
\code{None}, the identity function is assumed, that is, all elements of
|
|
\var{iterable} that are false are removed.
|
|
|
|
Note that \code{filter(function, \var{iterable})} is equivalent to
|
|
\code{[item for item in \var{iterable} if function(item)]} if function is
|
|
not \code{None} and \code{[item for item in \var{iterable} if item]} if
|
|
function is \code{None}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{float}{\optional{x}}
|
|
Convert a string or a number to floating point. If the argument is a
|
|
string, it must contain a possibly signed decimal or floating point
|
|
number, possibly embedded in whitespace. Otherwise, the argument may be a plain
|
|
or long integer or a floating point number, and a floating point
|
|
number with the same value (within Python's floating point
|
|
precision) is returned. If no argument is given, returns \code{0.0}.
|
|
|
|
\note{When passing in a string, values for NaN\index{NaN}
|
|
and Infinity\index{Infinity} may be returned, depending on the
|
|
underlying C library. The specific set of strings accepted which
|
|
cause these values to be returned depends entirely on the C library
|
|
and is known to vary.}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{frozenset}{\optional{iterable}}
|
|
Return a frozenset object whose elements are taken from \var{iterable}.
|
|
Frozensets are sets that have no update methods but can be hashed and
|
|
used as members of other sets or as dictionary keys. The elements of
|
|
a frozenset must be immutable themselves. To represent sets of sets,
|
|
the inner sets should also be \class{frozenset} objects. If
|
|
\var{iterable} is not specified, returns a new empty set,
|
|
\code{frozenset([])}.
|
|
\versionadded{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{getattr}{object, name\optional{, default}}
|
|
Return the value of the named attributed of \var{object}. \var{name}
|
|
must be a string. If the string is the name of one of the object's
|
|
attributes, the result is the value of that attribute. For example,
|
|
\code{getattr(x, 'foobar')} is equivalent to \code{x.foobar}. If the
|
|
named attribute does not exist, \var{default} is returned if provided,
|
|
otherwise \exception{AttributeError} is raised.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{globals}{}
|
|
Return a dictionary representing the current global symbol table.
|
|
This is always the dictionary of the current module (inside a
|
|
function or method, this is the module where it is defined, not the
|
|
module from which it is called).
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{hasattr}{object, name}
|
|
The arguments are an object and a string. The result is \code{True} if the
|
|
string is the name of one of the object's attributes, \code{False} if not.
|
|
(This is implemented by calling \code{getattr(\var{object},
|
|
\var{name})} and seeing whether it raises an exception or not.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{hash}{object}
|
|
Return the hash value of the object (if it has one). Hash values
|
|
are integers. They are used to quickly compare dictionary
|
|
keys during a dictionary lookup. Numeric values that compare equal
|
|
have the same hash value (even if they are of different types, as is
|
|
the case for 1 and 1.0).
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{help}{\optional{object}}
|
|
Invoke the built-in help system. (This function is intended for
|
|
interactive use.) If no argument is given, the interactive help
|
|
system starts on the interpreter console. If the argument is a
|
|
string, then the string is looked up as the name of a module,
|
|
function, class, method, keyword, or documentation topic, and a
|
|
help page is printed on the console. If the argument is any other
|
|
kind of object, a help page on the object is generated.
|
|
\versionadded{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{hex}{x}
|
|
Convert an integer number (of any size) to a hexadecimal string.
|
|
The result is a valid Python expression.
|
|
\versionchanged[Formerly only returned an unsigned literal]{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{id}{object}
|
|
Return the ``identity'' of an object. This is an integer (or long
|
|
integer) which is guaranteed to be unique and constant for this
|
|
object during its lifetime. Two objects with non-overlapping lifetimes
|
|
may have the same \function{id()} value. (Implementation
|
|
note: this is the address of the object.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{input}{\optional{prompt}}
|
|
Equivalent to \code{eval(raw_input(\var{prompt}))}.
|
|
\warning{This function is not safe from user errors! It
|
|
expects a valid Python expression as input; if the input is not
|
|
syntactically valid, a \exception{SyntaxError} will be raised.
|
|
Other exceptions may be raised if there is an error during
|
|
evaluation. (On the other hand, sometimes this is exactly what you
|
|
need when writing a quick script for expert use.)}
|
|
|
|
If the \refmodule{readline} module was loaded, then
|
|
\function{input()} will use it to provide elaborate line editing and
|
|
history features.
|
|
|
|
Consider using the \function{raw_input()} function for general input
|
|
from users.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{int}{\optional{x\optional{, radix}}}
|
|
Convert a string or number to a plain integer. If the argument is a
|
|
string, it must contain a possibly signed decimal number
|
|
representable as a Python integer, possibly embedded in whitespace.
|
|
The \var{radix} parameter gives the base for the
|
|
conversion and may be any integer in the range [2, 36], or zero. If
|
|
\var{radix} is zero, the proper radix is guessed based on the
|
|
contents of string; the interpretation is the same as for integer
|
|
literals. If \var{radix} is specified and \var{x} is not a string,
|
|
\exception{TypeError} is raised.
|
|
Otherwise, the argument may be a plain or
|
|
long integer or a floating point number. Conversion of floating
|
|
point numbers to integers truncates (towards zero).
|
|
If the argument is outside the integer range a long object will
|
|
be returned instead. If no arguments are given, returns \code{0}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{isinstance}{object, classinfo}
|
|
Return true if the \var{object} argument is an instance of the
|
|
\var{classinfo} argument, or of a (direct or indirect) subclass
|
|
thereof. Also return true if \var{classinfo} is a type object
|
|
(new-style class) and \var{object} is an object of that type or of a
|
|
(direct or indirect) subclass thereof. If \var{object} is not a
|
|
class instance or an object of the given type, the function always
|
|
returns false. If \var{classinfo} is neither a class object nor a
|
|
type object, it may be a tuple of class or type objects, or may
|
|
recursively contain other such tuples (other sequence types are not
|
|
accepted). If \var{classinfo} is not a class, type, or tuple of
|
|
classes, types, and such tuples, a \exception{TypeError} exception
|
|
is raised.
|
|
\versionchanged[Support for a tuple of type information was added]{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{issubclass}{class, classinfo}
|
|
Return true if \var{class} is a subclass (direct or indirect) of
|
|
\var{classinfo}. A class is considered a subclass of itself.
|
|
\var{classinfo} may be a tuple of class objects, in which case every
|
|
entry in \var{classinfo} will be checked. In any other case, a
|
|
\exception{TypeError} exception is raised.
|
|
\versionchanged[Support for a tuple of type information was added]{2.3}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{iter}{o\optional{, sentinel}}
|
|
Return an iterator object. The first argument is interpreted very
|
|
differently depending on the presence of the second argument.
|
|
Without a second argument, \var{o} must be a collection object which
|
|
supports the iteration protocol (the \method{__iter__()} method), or
|
|
it must support the sequence protocol (the \method{__getitem__()}
|
|
method with integer arguments starting at \code{0}). If it does not
|
|
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()}
|
|
method; if the value returned is equal to \var{sentinel},
|
|
\exception{StopIteration} will be raised, otherwise the value will
|
|
be returned.
|
|
\versionadded{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{len}{s}
|
|
Return the length (the number of items) of an object. The argument
|
|
may be a sequence (string, tuple or list) or a mapping (dictionary).
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{list}{\optional{iterable}}
|
|
Return a list whose items are the same and in the same order as
|
|
\var{iterable}'s items. \var{iterable} may be either a sequence, a
|
|
container that supports iteration, or an iterator object. If
|
|
\var{iterable} is already a list, a copy is made and returned,
|
|
similar to \code{\var{iterable}[:]}. For instance,
|
|
\code{list('abc')} returns \code{['a', 'b', 'c']} and \code{list(
|
|
(1, 2, 3) )} returns \code{[1, 2, 3]}. If no argument is given,
|
|
returns a new empty list, \code{[]}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{locals}{}
|
|
Update and return a dictionary representing the current local symbol table.
|
|
\warning{The contents of this dictionary should not be modified;
|
|
changes may not affect the values of local variables used by the
|
|
interpreter.}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{long}{\optional{x\optional{, radix}}}
|
|
Convert a string or number to a long integer. If the argument is a
|
|
string, it must contain a possibly signed number of
|
|
arbitrary size, possibly embedded in whitespace. The
|
|
\var{radix} argument is interpreted in the same way as for
|
|
\function{int()}, and may only be given when \var{x} is a string.
|
|
Otherwise, the argument may be a plain or
|
|
long integer or a floating point number, and a long integer with
|
|
the same value is returned. Conversion of floating
|
|
point numbers to integers truncates (towards zero). If no arguments
|
|
are given, returns \code{0L}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{map}{function, iterable, ...}
|
|
Apply \var{function} to every item of \var{iterable} and return a list
|
|
of the results. If additional \var{iterable} arguments are passed,
|
|
\var{function} must take that many arguments and is applied to the
|
|
items from all iterables in parallel. If one iterable is shorter than another it
|
|
is assumed to be extended with \code{None} items. If \var{function}
|
|
is \code{None}, the identity function is assumed; if there are
|
|
multiple arguments, \function{map()} returns a list consisting
|
|
of tuples containing the corresponding items from all iterables (a kind
|
|
of transpose operation). The \var{iterable} arguments may be a sequence
|
|
or any iterable object; the result is always a list.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{max}{iterable\optional{, args...}\optional{key}}
|
|
With a single argument \var{iterable}, return the largest item of a
|
|
non-empty iterable (such as a string, tuple or list). With more
|
|
than one argument, return the largest of the arguments.
|
|
|
|
The optional \var{key} argument specifies a one-argument ordering
|
|
function like that used for \method{list.sort()}. The \var{key}
|
|
argument, if supplied, must be in keyword form (for example,
|
|
\samp{max(a,b,c,key=func)}).
|
|
\versionchanged[Added support for the optional \var{key} argument]{2.5}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{min}{iterable\optional{, args...}\optional{key}}
|
|
With a single argument \var{iterable}, return the smallest item of a
|
|
non-empty iterable (such as a string, tuple or list). With more
|
|
than one argument, return the smallest of the arguments.
|
|
|
|
The optional \var{key} argument specifies a one-argument ordering
|
|
function like that used for \method{list.sort()}. The \var{key}
|
|
argument, if supplied, must be in keyword form (for example,
|
|
\samp{min(a,b,c,key=func)}).
|
|
\versionchanged[Added support for the optional \var{key} argument]{2.5}
|
|
\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
|
|
to all instances of new style classes.
|
|
\versionadded{2.2}
|
|
|
|
\versionchanged[This function does not accept any arguments.
|
|
Formerly, it accepted arguments but ignored them]{2.3}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{oct}{x}
|
|
Convert an integer number (of any size) to an octal string. The
|
|
result is a valid Python expression.
|
|
\versionchanged[Formerly only returned an unsigned literal]{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{open}{filename\optional{, mode\optional{, bufsize}}}
|
|
Open a file, returning an object of the \class{file} type described
|
|
in section~\ref{bltin-file-objects}, ``\ulink{File
|
|
Objects}{bltin-file-objects.html}''. If the file cannot be opened,
|
|
\exception{IOError} is raised. When opening a file, it's
|
|
preferable to use \function{open()} instead of invoking the
|
|
\class{file} constructor directly.
|
|
|
|
The first two arguments are the same as for \code{stdio}'s
|
|
\cfunction{fopen()}: \var{filename} is the file name to be opened,
|
|
and \var{mode} is a string indicating how the file is to be opened.
|
|
|
|
The most commonly-used values of \var{mode} are \code{'r'} for
|
|
reading, \code{'w'} for writing (truncating the file if it already
|
|
exists), and \code{'a'} for appending (which on \emph{some} \UNIX{}
|
|
systems means that \emph{all} writes append to the end of the file
|
|
regardless of the current seek position). If \var{mode} is omitted,
|
|
it defaults to \code{'r'}. When opening a binary file, you should
|
|
append \code{'b'} to the \var{mode} value to open the file in binary
|
|
mode, which will improve portability. (Appending \code{'b'} is
|
|
useful even on systems that don't treat binary and text files
|
|
differently, where it serves as documentation.) See below for more
|
|
possible values of \var{mode}.
|
|
|
|
\index{line-buffered I/O}\index{unbuffered I/O}\index{buffer size, I/O}
|
|
\index{I/O control!buffering}
|
|
The optional \var{bufsize} argument specifies the
|
|
file's desired buffer size: 0 means unbuffered, 1 means line
|
|
buffered, any other positive value means use a buffer of
|
|
(approximately) that size. A negative \var{bufsize} means to use
|
|
the system default, which is usually line buffered for tty
|
|
devices and fully buffered for other files. If omitted, the system
|
|
default is used.\footnote{
|
|
Specifying a buffer size currently has no effect on systems that
|
|
don't have \cfunction{setvbuf()}. The interface to specify the
|
|
buffer size is not done using a method that calls
|
|
\cfunction{setvbuf()}, because that may dump core when called
|
|
after any I/O has been performed, and there's no reliable way to
|
|
determine whether this is the case.}
|
|
|
|
Modes \code{'r+'}, \code{'w+'} and \code{'a+'} open the file for
|
|
updating (note that \code{'w+'} truncates the file). Append
|
|
\code{'b'} to the mode to open the file in binary mode, on systems
|
|
that differentiate between binary and text files; on systems
|
|
that don't have this distinction, adding the \code{'b'} has no effect.
|
|
|
|
In addition to the standard \cfunction{fopen()} values \var{mode}
|
|
may be \code{'U'} or \code{'rU'}. Python is usually built with universal
|
|
newline support; supplying \code{'U'} opens the file as a text file, but
|
|
lines may be terminated by any of the following: the \UNIX{} end-of-line
|
|
convention \code{'\e n'},
|
|
the Macintosh convention \code{'\e r'}, or the Windows
|
|
convention \code{'\e r\e n'}. All of these external representations are seen as
|
|
\code{'\e n'}
|
|
by the Python program. If Python is built without universal newline support
|
|
a \var{mode} with \code{'U'} is the same as normal text mode. Note that
|
|
file objects so opened also have an attribute called
|
|
\member{newlines} which has a value of \code{None} (if no newlines
|
|
have yet been seen), \code{'\e n'}, \code{'\e r'}, \code{'\e r\e n'},
|
|
or a tuple containing all the newline types seen.
|
|
|
|
Python enforces that the mode, after stripping \code{'U'}, begins with
|
|
\code{'r'}, \code{'w'} or \code{'a'}.
|
|
|
|
\versionchanged[Restriction on first letter of mode string
|
|
introduced]{2.5}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{ord}{c}
|
|
Given a string of length one, return an integer representing the
|
|
Unicode code point of the character when the argument is a unicode object,
|
|
or the value of the byte when the argument is an 8-bit string.
|
|
For example, \code{ord('a')} returns the integer \code{97},
|
|
\code{ord(u'\e u2020')} returns \code{8224}. This is the inverse of
|
|
\function{chr()} for 8-bit strings and of \function{unichr()} for unicode
|
|
objects. If a unicode argument is given and Python was built with
|
|
UCS2 Unicode, then the character's code point must be in the range
|
|
[0..65535] inclusive; otherwise the string length is two, and a
|
|
\exception{TypeError} will be raised.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{pow}{x, y\optional{, z}}
|
|
Return \var{x} to the power \var{y}; if \var{z} is present, return
|
|
\var{x} to the power \var{y}, modulo \var{z} (computed more
|
|
efficiently than \code{pow(\var{x}, \var{y}) \%\ \var{z}}).
|
|
The two-argument form \code{pow(\var{x}, \var{y})} is equivalent to using
|
|
the power operator: \code{\var{x}**\var{y}}.
|
|
|
|
The arguments must have numeric types. With mixed operand types, the
|
|
coercion rules for binary arithmetic operators apply. For int and
|
|
long int operands, the result has the same type as the operands
|
|
(after coercion) unless the second argument is negative; in that
|
|
case, all arguments are converted to float and a float result is
|
|
delivered. For example, \code{10**2} returns \code{100}, but
|
|
\code{10**-2} returns \code{0.01}. (This last feature was added in
|
|
Python 2.2. In Python 2.1 and before, if both arguments were of integer
|
|
types and the second argument was negative, an exception was raised.)
|
|
If the second argument is negative, the third argument must be omitted.
|
|
If \var{z} is present, \var{x} and \var{y} must be of integer types,
|
|
and \var{y} must be non-negative. (This restriction was added in
|
|
Python 2.2. In Python 2.1 and before, floating 3-argument \code{pow()}
|
|
returned platform-dependent results depending on floating-point
|
|
rounding accidents.)
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{property}{\optional{fget\optional{, fset\optional{,
|
|
fdel\optional{, doc}}}}}
|
|
Return a property attribute for new-style classes (classes that
|
|
derive from \class{object}).
|
|
|
|
\var{fget} is a function for getting an attribute value, likewise
|
|
\var{fset} is a function for setting, and \var{fdel} a function
|
|
for del'ing, an attribute. Typical use is to define a managed attribute x:
|
|
|
|
\begin{verbatim}
|
|
class C(object):
|
|
def __init__(self): self._x = None
|
|
def getx(self): return self._x
|
|
def setx(self, value): self._x = value
|
|
def delx(self): del self._x
|
|
x = property(getx, setx, delx, "I'm the 'x' property.")
|
|
\end{verbatim}
|
|
|
|
If given, \var{doc} will be the docstring of the property attribute.
|
|
Otherwise, the property will copy \var{fget}'s docstring (if it
|
|
exists). This makes it possible to create read-only properties
|
|
easily using \function{property()} as a decorator:
|
|
|
|
\begin{verbatim}
|
|
class Parrot(object):
|
|
def __init__(self):
|
|
self._voltage = 100000
|
|
|
|
@property
|
|
def voltage(self):
|
|
"""Get the current voltage."""
|
|
return self._voltage
|
|
\end{verbatim}
|
|
|
|
turns the \method{voltage()} method into a ``getter'' for a read-only
|
|
attribute with the same name.
|
|
|
|
\versionadded{2.2}
|
|
\versionchanged[Use \var{fget}'s docstring if no \var{doc} given]{2.5}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{range}{\optional{start,} stop\optional{, step}}
|
|
This is a versatile function to create lists containing arithmetic
|
|
progressions. It is most often used in \keyword{for} loops. The
|
|
arguments must be plain integers. If the \var{step} argument is
|
|
omitted, it defaults to \code{1}. If the \var{start} argument is
|
|
omitted, it defaults to \code{0}. The full form returns a list of
|
|
plain integers \code{[\var{start}, \var{start} + \var{step},
|
|
\var{start} + 2 * \var{step}, \ldots]}. If \var{step} is positive,
|
|
the last element is the largest \code{\var{start} + \var{i} *
|
|
\var{step}} less than \var{stop}; if \var{step} is negative, the last
|
|
element is the smallest \code{\var{start} + \var{i} * \var{step}}
|
|
greater than \var{stop}. \var{step} must not be zero (or else
|
|
\exception{ValueError} is raised). Example:
|
|
|
|
\begin{verbatim}
|
|
>>> range(10)
|
|
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
|
|
>>> range(1, 11)
|
|
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
|
|
>>> range(0, 30, 5)
|
|
[0, 5, 10, 15, 20, 25]
|
|
>>> range(0, 10, 3)
|
|
[0, 3, 6, 9]
|
|
>>> range(0, -10, -1)
|
|
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
|
|
>>> range(0)
|
|
[]
|
|
>>> range(1, 0)
|
|
[]
|
|
\end{verbatim}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{raw_input}{\optional{prompt}}
|
|
If the \var{prompt} argument is present, it is written to standard output
|
|
without a trailing newline. The function then reads a line from input,
|
|
converts it to a string (stripping a trailing newline), and returns that.
|
|
When \EOF{} is read, \exception{EOFError} is raised. Example:
|
|
|
|
\begin{verbatim}
|
|
>>> s = raw_input('--> ')
|
|
--> Monty Python's Flying Circus
|
|
>>> s
|
|
"Monty Python's Flying Circus"
|
|
\end{verbatim}
|
|
|
|
If the \refmodule{readline} module was loaded, then
|
|
\function{raw_input()} will use it to provide elaborate
|
|
line editing and history features.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{reduce}{function, iterable\optional{, initializer}}
|
|
Apply \var{function} of two arguments cumulatively to the items of
|
|
\var{iterable}, from left to right, so as to reduce the iterable to
|
|
a single value. For example, \code{reduce(lambda x, y: x+y, [1, 2,
|
|
3, 4, 5])} calculates \code{((((1+2)+3)+4)+5)}. The left argument,
|
|
\var{x}, is the accumulated value and the right argument, \var{y},
|
|
is the update value from the \var{iterable}. If the optional
|
|
\var{initializer} is present, it is placed before the items of the
|
|
iterable in the calculation, and serves as a default when the
|
|
iterable is empty. If \var{initializer} is not given and
|
|
\var{iterable} contains only one item, the first item is returned.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{reload}{module}
|
|
Reload a previously imported \var{module}. The
|
|
argument must be a module object, so it must have been successfully
|
|
imported before. This is useful if you have edited the module
|
|
source file using an external editor and want to try out the new
|
|
version without leaving the Python interpreter. The return value is
|
|
the module object (the same as the \var{module} argument).
|
|
|
|
When \code{reload(module)} is executed:
|
|
|
|
\begin{itemize}
|
|
|
|
\item Python modules' code is recompiled and the module-level code
|
|
reexecuted, defining a new set of objects which are bound to names in
|
|
the module's dictionary. The \code{init} function of extension
|
|
modules is not called a second time.
|
|
|
|
\item As with all other objects in Python the old objects are only
|
|
reclaimed after their reference counts drop to zero.
|
|
|
|
\item The names in the module namespace are updated to point to
|
|
any new or changed objects.
|
|
|
|
\item Other references to the old objects (such as names external
|
|
to the module) are not rebound to refer to the new objects and
|
|
must be updated in each namespace where they occur if that is
|
|
desired.
|
|
|
|
\end{itemize}
|
|
|
|
There are a number of other caveats:
|
|
|
|
If a module is syntactically correct but its initialization fails,
|
|
the first \keyword{import} statement for it does not bind its name
|
|
locally, but does store a (partially initialized) module object in
|
|
\code{sys.modules}. To reload the module you must first
|
|
\keyword{import} it again (this will bind the name to the partially
|
|
initialized module object) before you can \function{reload()} it.
|
|
|
|
When a module is reloaded, its dictionary (containing the module's
|
|
global variables) is retained. Redefinitions of names will override
|
|
the old definitions, so this is generally not a problem. If the new
|
|
version of a module does not define a name that was defined by the
|
|
old version, the old definition remains. This feature can be used
|
|
to the module's advantage if it maintains a global table or cache of
|
|
objects --- with a \keyword{try} statement it can test for the
|
|
table's presence and skip its initialization if desired:
|
|
|
|
\begin{verbatim}
|
|
try:
|
|
cache
|
|
except NameError:
|
|
cache = {}
|
|
\end{verbatim}
|
|
|
|
|
|
It is legal though generally not very useful to reload built-in or
|
|
dynamically loaded modules, except for \refmodule{sys},
|
|
\refmodule[main]{__main__} and \refmodule[builtin]{__builtin__}. In
|
|
many cases, however, extension modules are not designed to be
|
|
initialized more than once, and may fail in arbitrary ways when
|
|
reloaded.
|
|
|
|
If a module imports objects from another module using \keyword{from}
|
|
\ldots{} \keyword{import} \ldots{}, calling \function{reload()} for
|
|
the other module does not redefine the objects imported from it ---
|
|
one way around this is to re-execute the \keyword{from} statement,
|
|
another is to use \keyword{import} and qualified names
|
|
(\var{module}.\var{name}) instead.
|
|
|
|
If a module instantiates instances of a class, reloading the module
|
|
that defines the class does not affect the method definitions of the
|
|
instances --- they continue to use the old class definition. The
|
|
same is true for derived classes.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{repr}{object}
|
|
Return a string containing a printable representation of an object.
|
|
This is the same value yielded by conversions (reverse quotes).
|
|
It is sometimes useful to be able to access this operation as an
|
|
ordinary function. For many types, this function makes an attempt
|
|
to return a string that would yield an object with the same value
|
|
when passed to \function{eval()}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{reversed}{seq}
|
|
Return a reverse iterator. \var{seq} must be an object which
|
|
supports the sequence protocol (the __len__() method and the
|
|
\method{__getitem__()} method with integer arguments starting at
|
|
\code{0}).
|
|
\versionadded{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{round}{x\optional{, n}}
|
|
Return the floating point value \var{x} rounded to \var{n} digits
|
|
after the decimal point. If \var{n} is omitted, it defaults to zero.
|
|
The result is a floating point number. Values are rounded to the
|
|
closest multiple of 10 to the power minus \var{n}; if two multiples
|
|
are equally close, rounding is done away from 0 (so. for example,
|
|
\code{round(0.5)} is \code{1.0} and \code{round(-0.5)} is \code{-1.0}).
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{set}{\optional{iterable}}
|
|
Return a set whose elements are taken from \var{iterable}. The elements
|
|
must be immutable. To represent sets of sets, the inner sets should
|
|
be \class{frozenset} objects. If \var{iterable} is not specified,
|
|
returns a new empty set, \code{set([])}.
|
|
\versionadded{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{setattr}{object, name, value}
|
|
This is the counterpart of \function{getattr()}. The arguments are an
|
|
object, a string and an arbitrary value. The string may name an
|
|
existing attribute or a new attribute. The function assigns the
|
|
value to the attribute, provided the object allows it. For example,
|
|
\code{setattr(\var{x}, '\var{foobar}', 123)} is equivalent to
|
|
\code{\var{x}.\var{foobar} = 123}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{slice}{\optional{start,} stop\optional{, step}}
|
|
Return a slice object representing the set of indices specified by
|
|
\code{range(\var{start}, \var{stop}, \var{step})}. The \var{start}
|
|
and \var{step} arguments default to \code{None}. Slice objects have
|
|
read-only data attributes \member{start}, \member{stop} and
|
|
\member{step} which merely return the argument values (or their
|
|
default). They have no other explicit functionality; however they
|
|
are used by Numerical Python\index{Numerical Python} and other third
|
|
party extensions. Slice objects are also generated when extended
|
|
indexing syntax is used. For example: \samp{a[start:stop:step]} or
|
|
\samp{a[start:stop, i]}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{sorted}{iterable\optional{, cmp\optional{,
|
|
key\optional{, reverse}}}}
|
|
Return a new sorted list from the items in \var{iterable}.
|
|
|
|
The optional arguments \var{cmp}, \var{key}, and \var{reverse} have
|
|
the same meaning as those for the \method{list.sort()} method
|
|
(described in section~\ref{typesseq-mutable}).
|
|
|
|
\var{cmp} specifies a custom comparison function of two arguments
|
|
(iterable elements) which should return a negative, zero or positive
|
|
number depending on whether the first argument is considered smaller
|
|
than, equal to, or larger than the second argument:
|
|
\samp{\var{cmp}=\keyword{lambda} \var{x},\var{y}:
|
|
\function{cmp}(x.lower(), y.lower())}
|
|
|
|
\var{key} specifies a function of one argument that is used to
|
|
extract a comparison key from each list element:
|
|
\samp{\var{key}=\function{str.lower}}
|
|
|
|
\var{reverse} is a boolean value. If set to \code{True}, then the
|
|
list elements are sorted as if each comparison were reversed.
|
|
|
|
In general, the \var{key} and \var{reverse} conversion processes are
|
|
much faster than specifying an equivalent \var{cmp} function. This is
|
|
because \var{cmp} is called multiple times for each list element while
|
|
\var{key} and \var{reverse} touch each element only once.
|
|
|
|
\versionadded{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{staticmethod}{function}
|
|
Return a static method for \var{function}.
|
|
|
|
A static method does not receive an implicit first argument.
|
|
To declare a static method, use this idiom:
|
|
|
|
\begin{verbatim}
|
|
class C:
|
|
@staticmethod
|
|
def f(arg1, arg2, ...): ...
|
|
\end{verbatim}
|
|
|
|
The \code{@staticmethod} form is a function decorator -- see the description
|
|
of function definitions in chapter 7 of the
|
|
\citetitle[../ref/function.html]{Python Reference Manual} for details.
|
|
|
|
It can be called either on the class (such as \code{C.f()}) or on an
|
|
instance (such as \code{C().f()}). The instance is ignored except
|
|
for its class.
|
|
|
|
Static methods in Python are similar to those found in Java or \Cpp.
|
|
For a more advanced concept, see \function{classmethod()} in this
|
|
section.
|
|
|
|
For more information on static methods, consult the documentation on the
|
|
standard type hierarchy in chapter 3 of the
|
|
\citetitle[../ref/types.html]{Python Reference Manual} (at the bottom).
|
|
\versionadded{2.2}
|
|
\versionchanged[Function decorator syntax added]{2.4}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{str}{\optional{object}}
|
|
Return a string containing a nicely printable representation of an
|
|
object. For strings, this returns the string itself. The
|
|
difference with \code{repr(\var{object})} is that
|
|
\code{str(\var{object})} does not always attempt to return a string
|
|
that is acceptable to \function{eval()}; its goal is to return a
|
|
printable string. If no argument is given, returns the empty
|
|
string, \code{''}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{sum}{iterable\optional{, start}}
|
|
Sums \var{start} and the items of an \var{iterable} from left to
|
|
right and returns the total. \var{start} defaults to \code{0}.
|
|
The \var{iterable}'s items are normally numbers, and are not allowed
|
|
to be strings. The fast, correct way to concatenate a sequence of
|
|
strings is by calling \code{''.join(\var{sequence})}.
|
|
Note that \code{sum(range(\var{n}), \var{m})} is equivalent to
|
|
\code{reduce(operator.add, range(\var{n}), \var{m})}
|
|
\versionadded{2.3}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{super}{type\optional{, object-or-type}}
|
|
Return the superclass of \var{type}. If the second argument is omitted
|
|
the super object returned is unbound. If the second argument is an
|
|
object, \code{isinstance(\var{obj}, \var{type})} must be true. If
|
|
the second argument is a type, \code{issubclass(\var{type2},
|
|
\var{type})} must be true.
|
|
\function{super()} only works for new-style classes.
|
|
|
|
A typical use for calling a cooperative superclass method is:
|
|
\begin{verbatim}
|
|
class C(B):
|
|
def meth(self, arg):
|
|
super(C, self).meth(arg)
|
|
\end{verbatim}
|
|
|
|
Note that \function{super} is implemented as part of the binding process for
|
|
explicit dotted attribute lookups such as
|
|
\samp{super(C, self).__getitem__(name)}. Accordingly, \function{super} is
|
|
undefined for implicit lookups using statements or operators such as
|
|
\samp{super(C, self)[name]}.
|
|
\versionadded{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{tuple}{\optional{iterable}}
|
|
Return a tuple whose items are the same and in the same order as
|
|
\var{iterable}'s items. \var{iterable} may be a sequence, a
|
|
container that supports iteration, or an iterator object.
|
|
If \var{iterable} is already a tuple, it
|
|
is returned unchanged. For instance, \code{tuple('abc')} returns
|
|
\code{('a', 'b', 'c')} and \code{tuple([1, 2, 3])} returns
|
|
\code{(1, 2, 3)}. If no argument is given, returns a new empty
|
|
tuple, \code{()}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{type}{object}
|
|
Return the type of an \var{object}. The return value is a
|
|
type\obindex{type} object. The \function{isinstance()} built-in
|
|
function is recommended for testing the type of an object.
|
|
|
|
With three arguments, \function{type} functions as a constructor
|
|
as detailed below.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{type}{name, bases, dict}
|
|
Return a new type object. This is essentially a dynamic form of the
|
|
\keyword{class} statement. The \var{name} string is the class name
|
|
and becomes the \member{__name__} attribute; the \var{bases} tuple
|
|
itemizes the base classes and becomes the \member{__bases__}
|
|
attribute; and the \var{dict} dictionary is the namespace containing
|
|
definitions for class body and becomes the \member{__dict__}
|
|
attribute. For example, the following two statements create
|
|
identical \class{type} objects:
|
|
|
|
\begin{verbatim}
|
|
>>> class X(object):
|
|
... a = 1
|
|
...
|
|
>>> X = type('X', (object,), dict(a=1))
|
|
\end{verbatim}
|
|
\versionadded{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{unichr}{i}
|
|
Return the Unicode string of one character whose Unicode code is the
|
|
integer \var{i}. For example, \code{unichr(97)} returns the string
|
|
\code{u'a'}. This is the inverse of \function{ord()} for Unicode
|
|
strings. The valid range for the argument depends how Python was
|
|
configured -- it may be either UCS2 [0..0xFFFF] or UCS4 [0..0x10FFFF].
|
|
\exception{ValueError} is raised otherwise.
|
|
\versionadded{2.0}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{unicode}{\optional{object\optional{, encoding
|
|
\optional{, errors}}}}
|
|
Return the Unicode string version of \var{object} using one of the
|
|
following modes:
|
|
|
|
If \var{encoding} and/or \var{errors} are given, \code{unicode()}
|
|
will decode the object which can either be an 8-bit string or a
|
|
character buffer using the codec for \var{encoding}. The
|
|
\var{encoding} parameter is a string giving the name of an encoding;
|
|
if the encoding is not known, \exception{LookupError} is raised.
|
|
Error handling is done according to \var{errors}; this specifies the
|
|
treatment of characters which are invalid in the input encoding. If
|
|
\var{errors} is \code{'strict'} (the default), a
|
|
\exception{ValueError} is raised on errors, while a value of
|
|
\code{'ignore'} causes errors to be silently ignored, and a value of
|
|
\code{'replace'} causes the official Unicode replacement character,
|
|
\code{U+FFFD}, to be used to replace input characters which cannot
|
|
be decoded. See also the \refmodule{codecs} module.
|
|
|
|
If no optional parameters are given, \code{unicode()} will mimic the
|
|
behaviour of \code{str()} except that it returns Unicode strings
|
|
instead of 8-bit strings. More precisely, if \var{object} is a
|
|
Unicode string or subclass it will return that Unicode string without
|
|
any additional decoding applied.
|
|
|
|
For objects which provide a \method{__unicode__()} method, it will
|
|
call this method without arguments to create a Unicode string. For
|
|
all other objects, the 8-bit string version or representation is
|
|
requested and then converted to a Unicode string using the codec for
|
|
the default encoding in \code{'strict'} mode.
|
|
|
|
\versionadded{2.0}
|
|
\versionchanged[Support for \method{__unicode__()} added]{2.2}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{vars}{\optional{object}}
|
|
Without arguments, return a dictionary corresponding to the current
|
|
local symbol table. With a module, class or class instance object
|
|
as argument (or anything else that has a \member{__dict__}
|
|
attribute), returns a dictionary corresponding to the object's
|
|
symbol table. The returned dictionary should not be modified: the
|
|
effects on the corresponding symbol table are undefined.\footnote{
|
|
In the current implementation, local variable bindings cannot
|
|
normally be affected this way, but variables retrieved from
|
|
other scopes (such as modules) can be. This may change.}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{xrange}{\optional{start,} stop\optional{, step}}
|
|
This function is very similar to \function{range()}, but returns an
|
|
``xrange object'' instead of a list. This is an opaque sequence
|
|
type which yields the same values as the corresponding list, without
|
|
actually storing them all simultaneously. The advantage of
|
|
\function{xrange()} over \function{range()} is minimal (since
|
|
\function{xrange()} still has to create the values when asked for
|
|
them) except when a very large range is used on a memory-starved
|
|
machine or when all of the range's elements are never used (such as
|
|
when the loop is usually terminated with \keyword{break}).
|
|
|
|
\note{\function{xrange()} is intended to be simple and fast.
|
|
Implementations may impose restrictions to achieve this.
|
|
The C implementation of Python restricts all arguments to
|
|
native C longs ("short" Python integers), and also requires
|
|
that the number of elements fit in a native C long.}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{zip}{\optional{iterable, \moreargs}}
|
|
This function returns a list of tuples, where the \var{i}-th tuple contains
|
|
the \var{i}-th element from each of the argument sequences or iterables.
|
|
The returned list is truncated in length to the length of
|
|
the shortest argument sequence. When there are multiple arguments
|
|
which are all of the same length, \function{zip()} is
|
|
similar to \function{map()} with an initial argument of \code{None}.
|
|
With a single sequence argument, it returns a list of 1-tuples.
|
|
With no arguments, it returns an empty list.
|
|
\versionadded{2.0}
|
|
|
|
\versionchanged[Formerly, \function{zip()} required at least one argument
|
|
and \code{zip()} raised a \exception{TypeError} instead of returning
|
|
an empty list]{2.4}
|
|
\end{funcdesc}
|
|
|
|
|
|
% ---------------------------------------------------------------------------
|
|
|
|
|
|
\section{Non-essential Built-in Functions \label{non-essential-built-in-funcs}}
|
|
|
|
There are several built-in functions that are no longer essential to learn,
|
|
know or use in modern Python programming. They have been kept here to
|
|
maintain backwards compatibility with programs written for older versions
|
|
of Python.
|
|
|
|
Python programmers, trainers, students and bookwriters should feel free to
|
|
bypass these functions without concerns about missing something important.
|
|
|
|
|
|
\setindexsubitem{(non-essential built-in functions)}
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|
|
|
\begin{funcdesc}{apply}{function, args\optional{, keywords}}
|
|
The \var{function} argument must be a callable object (a
|
|
user-defined or built-in function or method, or a class object) and
|
|
the \var{args} argument must be a sequence. The \var{function} is
|
|
called with \var{args} as the argument list; the number of arguments
|
|
is the length of the tuple.
|
|
If the optional \var{keywords} argument is present, it must be a
|
|
dictionary whose keys are strings. It specifies keyword arguments
|
|
to be added to the end of the argument list.
|
|
Calling \function{apply()} is different from just calling
|
|
\code{\var{function}(\var{args})}, since in that case there is always
|
|
exactly one argument. The use of \function{apply()} is equivalent
|
|
to \code{\var{function}(*\var{args}, **\var{keywords})}.
|
|
Use of \function{apply()} is not necessary since the ``extended call
|
|
syntax,'' as used in the last example, is completely equivalent.
|
|
|
|
\deprecated{2.3}{Use the extended call syntax instead, as described
|
|
above.}
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{buffer}{object\optional{, offset\optional{, size}}}
|
|
The \var{object} argument must be an object that supports the buffer
|
|
call interface (such as strings, arrays, and buffers). A new buffer
|
|
object will be created which references the \var{object} argument.
|
|
The buffer object will be a slice from the beginning of \var{object}
|
|
(or from the specified \var{offset}). The slice will extend to the
|
|
end of \var{object} (or will have a length given by the \var{size}
|
|
argument).
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{coerce}{x, y}
|
|
Return a tuple consisting of the two numeric arguments converted to
|
|
a common type, using the same rules as used by arithmetic
|
|
operations. If coercion is not possible, raise \exception{TypeError}.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{intern}{string}
|
|
Enter \var{string} in the table of ``interned'' strings and return
|
|
the interned string -- which is \var{string} itself or a copy.
|
|
Interning strings is useful to gain a little performance on
|
|
dictionary lookup -- if the keys in a dictionary are interned, and
|
|
the lookup key is interned, the key comparisons (after hashing) can
|
|
be done by a pointer compare instead of a string compare. Normally,
|
|
the names used in Python programs are automatically interned, and
|
|
the dictionaries used to hold module, class or instance attributes
|
|
have interned keys. \versionchanged[Interned strings are not
|
|
immortal (like they used to be in Python 2.2 and before);
|
|
you must keep a reference to the return value of \function{intern()}
|
|
around to benefit from it]{2.3}
|
|
\end{funcdesc}
|