Hello,

When using setup.py, it is possible to customize commands or use functions to get some results dynamically.

For instance, to run a post install script (that requires dependencies to be installed) one can write this:

class CustomInstallCommand(install):
    def _post_install(self):
        # Some stuff to do

    def __init__(self, *args, **kwargs):
        super(CustomInstallCommand, self).__init__(*args, **kwargs)
        atexit.register(self._post_install)

and use this class as keyword argument value in the setup() call:

cmdclass={'install': CustomInstallCommand}

(other commands like clean, test, tox can be customized this way too).

Second example, in order to compile translation files (po files) into mo files at setup time:

def create_mo_files():
    data_files = []
    # do stuff
    return data_files

and use the result as keyword argument value in the setup() call:

data_files=create_mo_files()

It looks quite obvious that it's not possible to do such things if one uses only a pyproject.toml file: how would it import a class or a function, or know about it, how to run it? (Or is there a way?)

From reading the code, I've seen that the keyword arguments list passed to setup() is hard coded (to build a sdist), so cmdclass and data_files are not usable at the moment (if I'm not wrong).

I guess this is not the easiest feature to implement. Is it planned or already discussed?