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This is Python version 3.3 alpha 0

Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 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.

Build Instructions

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

./configure make make test sudo make install

This will install Python as python3.

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.)

What's New

We try to have a comprehensive overview of the changes in the "What's New in Python 3.3" document, found at

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".


Documentation for Python 3.3 is online, updated daily:

It can also be downloaded in many formats for faster access. The documentation is downloadable in HTML, PDF, and reStructuredText formats; the latter version is primarily for documentation authors, translators, and people with special formatting requirements.

Converting From Python 2.x to 3.x

Python starting with 2.6 contains 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.

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. See for more information.


To test the interpreter, type "make test" in the top-level directory. 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.

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 -m 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 version. 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 2.6, 2.7 and 3.3 with 2.7 being the primary version, you would execute "make install" in your 2.7 build directory and "make altinstall" in the others.

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:

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

Release Schedule

See PEP 398 for release details:

Recent activity

Antoine Pitrou

Commits by Antoine Pitrou were pushed to python_mirrors/features/pep-3155

5a69119 - Issue #9957: SpooledTemporaryFile.truncate() now accepts an optional size parameter, as other file-like objects. Patch by Ryan Kelly.
Antoine Pitrou

Commits by Antoine Pitrou were pushed to python_mirrors/features/pep-3155

905b6f1 - Clarify concatenation behaviour of immutable strings, and remove explicit mention of the CPython optimization hack.
Antoine Pitrou

Commits by Antoine Pitrou were pushed to python_mirrors/features/pep-3155

2d6f0e2 - Clarify concatenation behaviour of immutable strings, and remove explicit mention of the CPython optimization hack.
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