Here is a list of the basic steps necessary to get set up and make a patch:
Get a clone of CPython with hg clone hg.python.org/cpython.
On UNIX, run ./configure --with-pydebug && make -j2 to build Python.
On Windows, load the project file PCbuild\pcbuild.sln in Visual Studio, select Debug, and Build ‣ Build Solution.
Run the tests with ./python -m test -j3 (use ./python.exe on most Mac OS X systems and PCbuild\python_d.exe on Windows; replace test with test.regrtest for 2.7).
Make the patch.
Submit it to the issue tracker.
Here are some links that you probably will reference frequently while contributing to Python.
We encourage everyone to contribute to Python and that’s why we have put up this developer’s guide. If you still have questions after reviewing the material in this guide, then the Python Mentors group is available to help guide new contributors through the process. The Developer FAQ is another useful source of information.
Guide for contributing to Python:
Getting Set Up
Where to Get Help
Lifecycle of a Patch
Running & Writing Tests
Following Python’s Development
It is recommended that the above documents be read in the order listed. You can stop where you feel comfortable and begin contributing immediately without reading and understanding these documents all at once. If you do choose to skip around within the documentation, be aware that it is written assuming preceding documentation has been read so you may find it necessary to backtrack to fill in missing concepts and terminology.
Improving Python’s code, documentation and tests are ongoing tasks that are never going to be “finished”, as Python operates as part of an ever-evolving system of technology. An even more challenging ongoing task than these necessary maintenance activities is finding ways to make Python, in the form of the standard library and the language definition, an even better tool in a developer’s toolkit.
While these kinds of change are much rarer than those described above, they do happen and that process is also described as part of this guide:
This guide is specifically for contributing to the Python reference interpreter, also known as CPython (while most of the standard library is written in Python, the interpreter core is written in C and integrates most easily with the C and C++ ecosystems).
There are other Python implementations, each with a different focus. Like CPython, they always have more things they would like to do than they have developers to work on them. Some major example that may be of interest are:
Anyone can clone this guide from hg.python.org/devguide/. Core developers should use ssh://hg@hg.python.org/devguide instead, so that they can push back their edits to the server.
Buildbot status
Python Developer FAQ
PEPs (Python Enhancement Proposals)
python.org maintenance
Developer Log
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Getting Set Up