Inline setuptools command to list requirements

setup.py

from setuptools import setup, Command

class ListRequirements(Command):
    """In-line command to display declared requirements."""
    # TODO:
    #   * Add option to write out in a format 
    #     comaptible with requirements.txt.
    #   * Add options to restrict to particular
    #     kinds & extras.
    user_options = []

    def initialize_options(self):
        pass

    def finalize_options(self):
        pass

    def run(self):
        d = self.distribution
        print('Requirements:\n  ', end='')
        print(*d.install_requires, sep='\n  ', end='\n\n')

        print('Extra requirements:')
        for k, v in sorted(d.extras_require.items()):
            print(k+':\n  ', end='')
            print(*v, sep='\n  ')
            print()

        print('Test requirements:\n  ', end='')
        print(*d.tests_require, sep='\n  ', end='\n\n')

        print('Setup requirements:\n  ', end='')
        print(*d.setup_requires, sep='\n  ', end='\n\n')
        
setup(
    ...
    cmdclass={'reqs': ListRequirements},
)