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Finished the GC section.

Browse source 
Removed all but one XXX.
Replaced 1.6 with 2.0.
Various minor corrections and additions.
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Andrew M. Kuchling 2000-06-30 01:44:05 +00:00
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Doc/whatsnew/whatsnew20.tex
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@ -1,7 +1,7 @@
\documentclass{howto} \documentclass{howto}
\title{What's New in Python 1.6} \title{What's New in Python 2.0}
\release{0.03} \release{0.04}
\author{A.M. Kuchling and Moshe Zadka} \author{A.M. Kuchling and Moshe Zadka}
\authoraddress{\email{amk1@bigfoot.com}, \email{moshez@math.huji.ac.il} } \authoraddress{\email{amk1@bigfoot.com}, \email{moshez@math.huji.ac.il} }
\begin{document} \begin{document}
@ -11,32 +11,27 @@
{\large This is a draft document; please report inaccuracies and {\large This is a draft document; please report inaccuracies and
omissions to the authors. This document should not be treated as omissions to the authors. This document should not be treated as
definitive; features described here might be removed or changed before definitive; features described here might be removed or changed during
Python 1.6final. \\ the beta cycle before the final release of Python 2.0.
XXX marks locations in the text where fact-checking or rewriting is
still needed.
} }
A new release of Python, version 1.6, will be released some time this A new release of Python, version 2.0, will be released some time this
summer. Alpha versions are already available from summer. Alpha versions are already available from
\url{http://www.python.org/1.6/}. This article talks about the \url{http://www.python.org/2.0/}. This article covers the exciting
exciting new features in 1.6, highlights some other useful changes, new features in 2.0, highlights some other useful changes, and points
and points out a few incompatible changes that may require rewriting out a few incompatible changes that may require rewriting code.
code.
Python's development never completely stops between releases, and a Python's development never completely stops between releases, and a
steady flow of bug fixes and improvements are always being submitted. steady flow of bug fixes and improvements are always being submitted.
A host of minor fixes, a few optimizations, additional docstrings, and A host of minor fixes, a few optimizations, additional docstrings, and
better error messages went into 1.6; to list them all would be better error messages went into 2.0; to list them all would be
impossible, but they're certainly significant. Consult the impossible, but they're certainly significant. Consult the
publicly-available CVS logs if you want to see the full list. publicly-available CVS logs if you want to see the full list.
% ====================================================================== % ======================================================================
\section{Unicode} \section{Unicode}
The largest new feature in Python 1.6 is a new fundamental data type: The largest new feature in Python 2.0 is a new fundamental data type:
Unicode strings. Unicode uses 16-bit numbers to represent characters Unicode strings. Unicode uses 16-bit numbers to represent characters
instead of the 8-bit number used by ASCII, meaning that 65,536 instead of the 8-bit number used by ASCII, meaning that 65,536
distinct characters can be supported. distinct characters can be supported.
@ -172,7 +167,7 @@ strings and provide only Unicode strings.
% ====================================================================== % ======================================================================
\section{Distutils: Making Modules Easy to Install} \section{Distutils: Making Modules Easy to Install}
Before Python 1.6, installing modules was a tedious affair -- there Before Python 2.0, installing modules was a tedious affair -- there
was no way to figure out automatically where Python is installed, or was no way to figure out automatically where Python is installed, or
what compiler options to use for extension modules. Software authors what compiler options to use for extension modules. Software authors
had to go through an ardous ritual of editing Makefiles and had to go through an ardous ritual of editing Makefiles and
@ -258,7 +253,7 @@ functions such as \function{string.replace()}, which takes 3 string
arguments, that means eight possible permutations, and correspondingly arguments, that means eight possible permutations, and correspondingly
complicated code. complicated code.
Instead, Python 1.6 pushes the problem onto the string type, making Instead, Python 2.0 pushes the problem onto the string type, making
string manipulation functionality available through methods on both string manipulation functionality available through methods on both
8-bit strings and Unicode strings. 8-bit strings and Unicode strings.
@ -279,27 +274,26 @@ The old \module{string} module is still around for backwards
compatibility, but it mostly acts as a front-end to the new string compatibility, but it mostly acts as a front-end to the new string
methods. methods.
Two methods which have no parallel in pre-1.6 versions, although they Two methods which have no parallel in pre-2.0 versions, although they
did exist in JPython for quite some time, are \method{startswith()} did exist in JPython for quite some time, are \method{startswith()}
and \method{endswith}. \code{s.startswith(t)} is equivalent to \code{s[:len(t)] and \method{endswith}. \code{s.startswith(t)} is equivalent to \code{s[:len(t)]
== t}, while \code{s.endswith(t)} is equivalent to \code{s[-len(t):] == t}. == t}, while \code{s.endswith(t)} is equivalent to \code{s[-len(t):] == t}.
(XXX what'll happen to join? is this even worth mentioning?) One %One other method which deserves special mention is \method{join}. The
other method which deserves special mention is \method{join}. The %\method{join} method of a string receives one parameter, a sequence of
\method{join} method of a string receives one parameter, a sequence of %strings, and is equivalent to the \function{string.join} function from
strings, and is equivalent to the \function{string.join} function from %the old \module{string} module, with the arguments reversed. In other
the old \module{string} module, with the arguments reversed. In other %words, \code{s.join(seq)} is equivalent to the old
words, \code{s.join(seq)} is equivalent to the old %\code{string.join(seq, s)}.
\code{string.join(seq, s)}.
% ====================================================================== % ======================================================================
\section{Porting to 1.6} \section{Porting to 2.0}
New Python releases try hard to be compatible with previous releases, New Python releases try hard to be compatible with previous releases,
and the record has been pretty good. However, some changes are and the record has been pretty good. However, some changes are
considered useful enough, often fixing initial design decisions that considered useful enough, often fixing initial design decisions that
turned to be actively mistaken, that breaking backward compatibility turned to be actively mistaken, that breaking backward compatibility
can't always be avoided. This section lists the changes in Python 1.6 can't always be avoided. This section lists the changes in Python 2.0
that may cause old Python code to break. that may cause old Python code to break.
The change which will probably break the most code is tightening up The change which will probably break the most code is tightening up
@ -307,7 +301,7 @@ the arguments accepted by some methods. Some methods would take
multiple arguments and treat them as a tuple, particularly various multiple arguments and treat them as a tuple, particularly various
list methods such as \method{.append()} and \method{.insert()}. list methods such as \method{.append()} and \method{.insert()}.
In earlier versions of Python, if \code{L} is a list, \code{L.append( In earlier versions of Python, if \code{L} is a list, \code{L.append(
1,2 )} appends the tuple \code{(1,2)} to the list. In Python 1.6 this 1,2 )} appends the tuple \code{(1,2)} to the list. In Python 2.0 this
causes a \exception{TypeError} exception to be raised, with the causes a \exception{TypeError} exception to be raised, with the
message: 'append requires exactly 1 argument; 2 given'. The fix is to message: 'append requires exactly 1 argument; 2 given'. The fix is to
simply add an extra set of parentheses to pass both values as a tuple: simply add an extra set of parentheses to pass both values as a tuple:
@ -315,10 +309,10 @@ simply add an extra set of parentheses to pass both values as a tuple:
The earlier versions of these methods were more forgiving because they The earlier versions of these methods were more forgiving because they
used an old function in Python's C interface to parse their arguments; used an old function in Python's C interface to parse their arguments;
1.6 modernizes them to use \function{PyArg_ParseTuple}, the current 2.0 modernizes them to use \function{PyArg_ParseTuple}, the current
argument parsing function, which provides more helpful error messages argument parsing function, which provides more helpful error messages
and treats multi-argument calls as errors. If you absolutely must use and treats multi-argument calls as errors. If you absolutely must use
1.6 but can't fix your code, you can edit \file{Objects/listobject.c} 2.0 but can't fix your code, you can edit \file{Objects/listobject.c}
and define the preprocessor symbol \code{NO_STRICT_LIST_APPEND} to and define the preprocessor symbol \code{NO_STRICT_LIST_APPEND} to
preserve the old behaviour; this isn't recommended. preserve the old behaviour; this isn't recommended.
@ -327,7 +321,7 @@ forgiving in this way. For example, \function{socket.connect(
('hostname', 25) )} is the correct form, passing a tuple representing ('hostname', 25) )} is the correct form, passing a tuple representing
an IP address, but \function{socket.connect( 'hostname', 25 )} also an IP address, but \function{socket.connect( 'hostname', 25 )} also
works. \function{socket.connect_ex()} and \function{socket.bind()} are works. \function{socket.connect_ex()} and \function{socket.bind()} are
similarly easy-going. 1.6alpha1 tightened these functions up, but similarly easy-going. 2.0alpha1 tightened these functions up, but
because the documentation actually used the erroneous multiple because the documentation actually used the erroneous multiple
argument form, many people wrote code which would break with the argument form, many people wrote code which would break with the
stricter checking. GvR backed out the changes in the face of public stricter checking. GvR backed out the changes in the face of public
@ -341,7 +335,7 @@ to allow reading files larger than 2Gb; this made the \method{tell()}
method of file objects return a long integer instead of a regular method of file objects return a long integer instead of a regular
integer. Some code would subtract two file offsets and attempt to use integer. Some code would subtract two file offsets and attempt to use
the result to multiply a sequence or slice a string, but this raised a the result to multiply a sequence or slice a string, but this raised a
\exception{TypeError}. In 1.6, long integers can be used to multiply \exception{TypeError}. In 2.0, long integers can be used to multiply
or slice a sequence, and it'll behave as you'd intuitively expect it or slice a sequence, and it'll behave as you'd intuitively expect it
to; \code{3L * 'abc'} produces 'abcabcabc', and \code{ to; \code{3L * 'abc'} produces 'abcabcabc', and \code{
(0,1,2,3)[2L:4L]} produces (2,3). Long integers can also be used in (0,1,2,3)[2L:4L]} produces (2,3). Long integers can also be used in
@ -353,7 +347,7 @@ of a long integer no longer has a trailing 'L' character, though
\function{repr()} still includes it. The 'L' annoyed many people who \function{repr()} still includes it. The 'L' annoyed many people who
wanted to print long integers that looked just like regular integers, wanted to print long integers that looked just like regular integers,
since they had to go out of their way to chop off the character. This since they had to go out of their way to chop off the character. This
is no longer a problem in 1.6, but code which assumes the 'L' is is no longer a problem in 2.0, but code which assumes the 'L' is
there, and does \code{str(longval)[:-1]} will now lose the final there, and does \code{str(longval)[:-1]} will now lose the final
digit. digit.
@ -367,8 +361,9 @@ For example, the number 8.1 can't be represented exactly in binary, so
\code{repr(8.1)} is \code{'8.0999999999999996'}, while str(8.1) is \code{repr(8.1)} is \code{'8.0999999999999996'}, while str(8.1) is
\code{'8.1'}. \code{'8.1'}.
%The \code{-X} command-line option, which turns all standard exceptions The \code{-X} command-line option, which turned all standard
%into strings instead of classes, has been removed. exceptions into strings instead of classes, has been removed;
the standard exceptions will now always be classes.
% ====================================================================== % ======================================================================
\section{Optional Collection of Cycles} \section{Optional Collection of Cycles}
@ -411,26 +406,22 @@ cycle if they have references to each other, causing all of the
objects to be leaked. objects to be leaked.
An experimental step has been made toward fixing this problem. When An experimental step has been made toward fixing this problem. When
compiling Python, the \code{--with-cycle-gc} (XXX correct option compiling Python, the \verb|--with-cycle-gc| option can be specified.
flag?) option can be specified. This causes a cycle detection This causes a cycle detection algorithm to be periodically executed,
algorithm to be periodically executed, which looks for inaccessible which looks for inaccessible cycles and deletes the objects involved.
cycles and deletes the objects involved.
Why isn't this enabled by default? Running the cycle detection Why isn't cycle detection enabled by default? Running the cycle detection
algorithm takes some time, and some tuning will be required to algorithm takes some time, and some tuning will be required to
minimize the overhead cost. It's not yet obvious how much performance minimize the overhead cost. It's not yet obvious how much performance
is lost, because benchmarking this is tricky and depends sensitively is lost, because benchmarking this is tricky and depends crucially
on how often the program creates and destroys objects. XXX is this on how often the program creates and destroys objects.
actually the correct reason? Or is it fear of breaking software that
runs happily while leaving garbage?
Several people worked on this problem. Early versions were written by Several people tackled this problem and contributed to a solution. An
XXX1, XXX2. (I vaguely remember several people writing first cuts at this. early implementation of the cycle detection approach was written by
Anyone recall who?) Toby Kelsey. The current algorithm was suggested by Eric Tiedemann
The implementation that's in Python 1.6 is a rewritten version, this during a visit to CNRI, and Guido van Rossum and Neil Schemenauer
time done by Neil Schemenauer. Lots of other people offered wrote two different implementations, which were later integrated by
suggestions along the way, such as (in alphabetical order) Neil. Lots of other people offered suggestions along the way; the
Marc-Andr\'e Lemburg, Tim Peters, Greg Stein, Eric Tiedemann. The
March 2000 archives of the python-dev mailing list contain most of the March 2000 archives of the python-dev mailing list contain most of the
relevant discussion, especially in the threads titled ``Reference relevant discussion, especially in the threads titled ``Reference
cycle collection for Python'' and ``Finalization again''. cycle collection for Python'' and ``Finalization again''.
@ -449,7 +440,7 @@ In Python 1.5 and earlier, you do this with the \function{apply()}
built-in function: \code{apply(f, \var{args}, \var{kw})} calls the built-in function: \code{apply(f, \var{args}, \var{kw})} calls the
function \function{f()} with the argument tuple \var{args} and the function \function{f()} with the argument tuple \var{args} and the
keyword arguments in the dictionary \var{kw}. Thanks to a patch from keyword arguments in the dictionary \var{kw}. Thanks to a patch from
Greg Ewing, 1.6 adds \code{f(*\var{args}, **\var{kw})} as a shorter Greg Ewing, 2.0 adds \code{f(*\var{args}, **\var{kw})} as a shorter
and clearer way to achieve the same effect. This syntax is and clearer way to achieve the same effect. This syntax is
symmetrical with the syntax for defining functions: symmetrical with the syntax for defining functions:
@ -516,8 +507,8 @@ An attempt has been made to alleviate one of Python's warts, the
often-confusing \exception{NameError} exception when code refers to a often-confusing \exception{NameError} exception when code refers to a
local variable before the variable has been assigned a value. For local variable before the variable has been assigned a value. For
example, the following code raises an exception on the \keyword{print} example, the following code raises an exception on the \keyword{print}
statement in both 1.5.2 and 1.6; in 1.5.2 a \exception{NameError} statement in both 1.5.2 and 2.0; in 1.5.2 a \exception{NameError}
exception is raised, while 1.6 raises a new exception is raised, while 2.0 raises a new
\exception{UnboundLocalError} exception. \exception{UnboundLocalError} exception.
\exception{UnboundLocalError} is a subclass of \exception{NameError}, \exception{UnboundLocalError} is a subclass of \exception{NameError},
so any existing code that expects \exception{NameError} to be raised so any existing code that expects \exception{NameError} to be raised
@ -533,7 +524,7 @@ f()
A new variable holding more detailed version information has been A new variable holding more detailed version information has been
added to the \module{sys} module. \code{sys.version_info} is a tuple added to the \module{sys} module. \code{sys.version_info} is a tuple
\code{(\var{major}, \var{minor}, \var{micro}, \var{level}, \code{(\var{major}, \var{minor}, \var{micro}, \var{level},
\var{serial})} For example, in 1.6a2 \code{sys.version_info} is \var{serial})} For example, in 2.0a2 \code{sys.version_info} is
\code{(1, 6, 0, 'alpha', 2)}. \var{level} is a string such as \code{(1, 6, 0, 'alpha', 2)}. \var{level} is a string such as
\code{"alpha"}, \code{"beta"}, or \code{""} for a final release. \code{"alpha"}, \code{"beta"}, or \code{""} for a final release.
@ -547,7 +538,7 @@ you can safely skip this section.
The version number of the Python C API was incremented, so C The version number of the Python C API was incremented, so C
extensions compiled for 1.5.2 must be recompiled in order to work with extensions compiled for 1.5.2 must be recompiled in order to work with
1.6. On Windows, attempting to import a third party extension built 2.0. On Windows, attempting to import a third party extension built
for Python 1.5.x usually results in an immediate crash; there's not for Python 1.5.x usually results in an immediate crash; there's not
much we can do about this. (XXX can anyone tell me why it crashes?) much we can do about this. (XXX can anyone tell me why it crashes?)
@ -581,7 +572,7 @@ Threading support on Windows was enhanced, too. Windows supports
thread locks that use kernel objects only in case of contention; in thread locks that use kernel objects only in case of contention; in
the common case when there's no contention, they use simpler functions the common case when there's no contention, they use simpler functions
which are an order of magnitude faster. A threaded version of Python which are an order of magnitude faster. A threaded version of Python
1.5.2 on NT is twice as slow as an unthreaded version; with the 1.6 1.5.2 on NT is twice as slow as an unthreaded version; with the 2.0
changes, the difference is only 10\%. These improvements were changes, the difference is only 10\%. These improvements were
contributed by Yakov Markovitch. contributed by Yakov Markovitch.
@ -626,7 +617,7 @@ is no longer compatible with operating systems that only have BSD
curses, but there don't seem to be any currently maintained OSes that curses, but there don't seem to be any currently maintained OSes that
fall into this category. fall into this category.
As mentioned in the earlier discussion of 1.6's Unicode support, the As mentioned in the earlier discussion of 2.0's Unicode support, the
underlying implementation of the regular expressions provided by the underlying implementation of the regular expressions provided by the
\module{re} module has been changed. SRE, a new regular expression \module{re} module has been changed. SRE, a new regular expression
engine written by Fredrik Lundh and partially funded by Hewlett engine written by Fredrik Lundh and partially funded by Hewlett
@ -637,7 +628,7 @@ strings.
\section{New modules} \section{New modules}
A number of new modules were added. We'll simply list them with brief A number of new modules were added. We'll simply list them with brief
descriptions; consult the 1.6 documentation for the details of a descriptions; consult the 2.0 documentation for the details of a
particular module. particular module.
\begin{itemize} \begin{itemize}
@ -675,10 +666,13 @@ checks Python source code for ambiguous indentation.
\item{\module{UserString}:} A base class useful for deriving objects that behave like strings. \item{\module{UserString}:} A base class useful for deriving objects that behave like strings.
\item{\module{winreg}:} An interface to the Windows registry. \item{\module{winreg} and \module{_wingreg}:} An interface to the
\module{winreg} has been part of PythonWin since 1995, but now has Windows registry. \module{winreg} has been part of PythonWin since
been added to the core distribution, and enhanced to support Unicode. 1995, but now has been added to the core distribution, and enhanced to
(Contributed by Bill Tutt and Mark Hammond.) support Unicode. \module{_winreg} is a low-level wrapper of the
Windows registry functions, contributed by Bill Tutt and Mark Hammond,
while \module{winreg} is a higher-level, more object-oriented API on top of
\module{_winreg}, designed by Thomas Heller and implemented by Paul Prescod.
\item{\module{zipfile}:} A module for reading and writing ZIP-format \item{\module{zipfile}:} A module for reading and writing ZIP-format
archives. These are archives produced by \program{PKZIP} on archives. These are archives produced by \program{PKZIP} on
@ -698,7 +692,7 @@ discussion on python-dev along the way.)
\section{IDLE Improvements} \section{IDLE Improvements}
IDLE is the official Python cross-platform IDE, written using Tkinter. IDLE is the official Python cross-platform IDE, written using Tkinter.
Python 1.6 includes IDLE 0.6, which adds a number of new features and Python 2.0 includes IDLE 0.6, which adds a number of new features and
improvements. A partial list: improvements. A partial list:
\begin{itemize} \begin{itemize}
@ -706,7 +700,7 @@ improvements. A partial list:
especially in the area of syntax highlighting and auto-indentation. especially in the area of syntax highlighting and auto-indentation.
\item The class browser now shows more information, such as the top \item The class browser now shows more information, such as the top
level functions in a module (XXX did I interpret that right?). level functions in a module.
\item Tab width is now a user settable option. When opening an existing Python \item Tab width is now a user settable option. When opening an existing Python
file, IDLE automatically detects the indentation conventions, and adapts. file, IDLE automatically detects the indentation conventions, and adapts.
@ -724,7 +718,7 @@ the vanilla Python interpreter.
\item In the editor window, there is now a line/column bar at the bottom. \item In the editor window, there is now a line/column bar at the bottom.
\item Three new keystroke commands: Check module (Alt-F5), Import \item Three new keystroke commands: Check module (Alt-F5), Import
module (F5) and Run script (Ctrl-F5) module (F5) and Run script (Ctrl-F5).
\end{itemize} \end{itemize}
@ -746,11 +740,13 @@ If you have code which relies on a module that's been moved to
to get them back, but you're encouraged to update any code that uses to get them back, but you're encouraged to update any code that uses
these modules. these modules.
XXX any others deleted? \section{Acknowledgements}
XXX Other candidates for deletion in 1.6: sgimodule.c, glmodule.c (and hence The author would like to thank the following people for offering suggestions on earlier drafts of this article:
cgenmodule.c), imgfile.c, svmodule.c, flmodule.c, fmmodule.c, almodule.c, clmodule.c, Skip Montanaro,
knee.py. Vladimir Marangozov,
Guido van Rossum,
Neil Schemenauer.
\end{document} \end{document}