getcmdclass

get_cmdclass, sometimes referred to as getcmdclass, is a helper function used in Python packaging to obtain a mapping of command names to their corresponding command classes. It is primarily associated with setuptools and distutils and is used to customize the behavior of commands invoked during package building and distribution, such as building extensions, creating source distributions, or generating metadata.

The function returns a dictionary that maps standard packaging commands (for example, build_py, build_ext, sdist, bdist_wheel, egg_info) to their Command subclass implementations. By retrieving this dictionary, a project can modify or extend the default command classes without redefining the entire cmdclass mapping. This enables granular customization while maintaining compatibility with the packaging tools in use.

Typical usage involves importing the helper, obtaining the default command class mapping, and then overriding specific entries with custom command classes. For example, a project might replace the build_ext command with a custom subclass to handle platform-specific compilation, while leaving other commands untouched. After modifying the dictionary, it is passed to setup() via the cmdclass parameter.

Example usage:

from setuptools import setup, get_cmdclass

from setuptools.command.build_ext import build_ext

cmdclass = get_cmdclass()

cmdclass['build_ext'] = build_ext

setup(cmdclass=cmdclass)

Notes and considerations:

- get_cmdclass provides a convenient way to extend packaging behavior in a way that remains compatible with the tools involved.

- In some environments or older setups, the function may not be available, in which case developers may construct their own cmdclass dictionary manually.

- The exact contents and behavior can vary between setuptools and distutils versions, so readers should consult their toolchain’s documentation for version-specific details.