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This is Python version 3.1 Release Candidate 2

Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Python Software Foundation. All rights reserved.

Python 3.x is a new version of the language, which is incompatible with the 2.x line of releases. The language is mostly the same, but many details, especially how built-in objects like dictionaries and strings work, have changed considerably, and a lot of deprecated features have finally been removed.

Release Schedule

See PEP 375 for release details:


Documentation for Python 3.1 is online, updated twice a day:

All documentation is also available online at the Python web site (, see below). It is available online for occasional reference, or can be downloaded in many formats for faster access. The documentation is downloadable in HTML, PostScript, PDF, LaTeX (through 2.5), and reStructuredText (2.6+) formats; the LaTeX and reStructuredText versions are primarily for documentation authors, translators, and people with special formatting requirements.

What's New

We try to have a comprehensive overview of the changes in the "What's New in Python 3.1" document, found at

Please help write it!

For a more detailed change log, read Misc/NEWS (though this file, too, is incomplete, and also doesn't list anything merged in from the 2.7 release under development).

If you want to install multiple versions of Python see the section below entitled "Installing multiple versions".

Proposals for enhancement

If you have a proposal to change Python, you may want to send an email to the comp.lang.python or python-ideas mailing lists for inital feedback. A Python Enhancement Proposal (PEP) may be submitted if your idea gains ground. All current PEPs, as well as guidelines for submitting a new PEP, are listed at

Converting From Python 2.x to 3.x

Python starting with 2.6 will contain features to help locating code that needs to be changed, such as optional warnings when deprecated features are used, and backported versions of certain key Python 3.x features.


To test the interpreter, type "make test" in the top-level directory. This runs the test set twice (once with no compiled files, once with the compiled files left by the previous test run). The test set produces some output. You can generally ignore the messages about skipped tests due to optional features which can't be imported. If a message is printed about a failed test or a traceback or core dump is produced, something is wrong. On some Linux systems (those that are not yet using glibc 6), test_strftime fails due to a non-standard implementation of strftime() in the C library. Please ignore this, or upgrade to glibc version 6.

By default, tests are prevented from overusing resources like disk space and memory. To enable these tests, run "make testall".

IMPORTANT: If the tests fail and you decide to mail a bug report, don't include the output of "make test". It is useless. Run the failing test manually, as follows:

./python Lib/test/ -v test_whatever

(substituting the top of the source tree for '.' if you built in a different directory). This runs the test in verbose mode.

Installing multiple versions

On Unix and Mac systems if you intend to install multiple versions of Python using the same installation prefix (--prefix argument to the configure script) you must take care that your primary python executable is not overwritten by the installation of a different versio. All files and directories installed using "make altinstall" contain the major and minor version and can thus live side-by-side. "make install" also creates ${prefix}/bin/python3 which refers to ${prefix}/bin/pythonX.Y. If you intend to install multiple versions using the same prefix you must decide which version (if any) is your "primary" version. Install that version using "make install". Install all other versions using "make altinstall".

For example, if you want to install Python 2.5, 2.6 and 3.0 with 2.6 being the primary version, you would execute "make install" in your 2.6 build directory and "make altinstall" in the others.

Configuration options and variables

A source-to-source translation tool, "2to3", can take care of the mundane task of converting large amounts of source code. It is not a complete solution but is complemented by the deprecation warnings in 2.6. This tool is currently available via the Subversion sandbox:

Issue Tracker and Mailing List

We're soliciting bug reports about all aspects of the language. Fixes are also welcome, preferable in unified diff format. Please use the issue tracker:

If you're not sure whether you're dealing with a bug or a feature, use the mailing list:

To subscribe to the list, use the mailman form:

Build Instructions

On Unix, Linux, BSD, OSX, and Cygwin:

./configure make make test sudo make install

You can pass many options to the configure script; run "./configure --help" to find out more. On OSX and Cygwin, the executable is called python.exe; elsewhere it's just python.

On Mac OS X, if you have configured Python with --enable-framework, you should use "make frameworkinstall" to do the installation. Note that this installs the Python executable in a place that is not normally on your PATH, you may want to set up a symlink in /usr/local/bin.

On Windows, see PCbuild/readme.txt.

If you wish, you can create a subdirectory and invoke configure from there. For example:

mkdir debug cd debug ../configure --with-pydebug make make test

(This will fail if you also built at the top-level directory. You should do a "make clean" at the toplevel first.)