What's the difference between setup.py and setup.cfg in python projects

Question

Need to know what's the difference between setup.py and setup.cfg. Both are used prominently in openstack projects

Answer 1

Traditionally, setup.py has been used to build a Python package, i.e.,

python setup.py build 

Like any old Python file, setup.py can contain lots of code. In most cases, however, it is purely declarative and simply lists package properties, e.g.,

from setuptools import setup  setup(     name="foobar",     version="0.1.0",     author="John Doe",     # ... ) 

In fact, some consider it bad style to put much logic in setup.py. To reflect that, setup.cfg (which is declarative by design) has become more popular for packaging:

[metadata] name = foobar version = 0.1.0 author = John Doe # ... 

This has the advantage that the packaging software (e.g., setuptools) doesn't need to evaluate a Python file to get the meta data, but can simply parse a config file.

You can add a dummy setup.py to that,

from setuptools import setup  if __name__ == "__main__":     setup() 

or go full PEP 517/518 and instead add a pyproject.toml.

[build-system] requires = ["setuptools>=42", "wheel"] build-backend = "setuptools.build_meta" 

You can then build your projects using pypa-build (pip install build) with

python3 -m build --sdist --wheel . 

That being said, the landscape of Python packaging software is very much in motion at the moment (2019/20/21) and it is not clear which will be the preferred method of defining a Python package in the future. For example, there is PEP 621 which suggests to put package metadata into pyproject.toml.