Fixes and improvements to CPython should first be contributed upstream. The Python Developer’s Guide is a great resource to guide you through the process.

That said, there are few scenarios where using python-cmake-buildsystem to patch CPython is relevant. Learn more about these at https://github.com/python-cmake-buildsystem/cpython.

By default, patches are applied at configuration time. Setting the option PYTHON_APPLY_PATCHES to OFF allows to change this. Note that the build system keep track which patches have been applied.

Each patch is documented by adding an entry to the README.rst file found in the same directory (or a parent directory). Whenever possible, references to bugs.python.org <http://bugs.python.org>`_(bpo) issues, corresponding `GitHub PRs and any related discussions on forums or mailing lists are also provided.

Patches are organized per python version. Patches specific to a system, a system+compiler, or a system+compiler+compiler_version are organized in corresponding sub-directories:

patches/<PY_VERSION_MAJOR>.<PY_VERSION_MINOR>
patches/<PYTHON_VERSION>
patches/<PYTHON_VERSION>/<CMAKE_SYSTEM_NAME>
patches/<PYTHON_VERSION>/<CMAKE_SYSTEM_NAME>-<CMAKE_C_COMPILER_ID>
patches/<PYTHON_VERSION>/<CMAKE_SYSTEM_NAME>-<CMAKE_C_COMPILER_ID>/<compiler_version>

where

• <PYTHON_VERSION> is of the form X.Y.Z
• <CMAKE_SYSTEM_NAME> is a value like Darwin, Linux or Windows. See corresponding CMake documentation for more details.
• <CMAKE_C_COMPILER_ID> is a valid like Clang, GNU or MSVC. See corresponding CMake documentation for more details.
• <compiler_version> is set to the value of CMAKE_C_COMPILER_VERSION (e.g 5.2.1) except when using Microsoft compiler where it is set to the value of MSVC_VERSION (e.g 1900).

Before being applied, patches are sorted alphabetically. This ensures that patch starting with 0001- is applied before the one starting with 0002-.

Note that for historical reasons, there are still patches found in cmake/patches and cmake/patches-win32 subdirectories. These will gradually be organized as described above.