Returns a list of all packages, each package has info about which package requires it and also its requirements.

packages.py

import json
import pkg_resources

packages = {}


for pkg in pkg_resources.working_set:
    packages[pkg.key.lower()] = {
        'requires': [req.project_name.lower() for req in pkg.requires()],
        'required_by': [],
    }


for pkg, data in packages.items():
    for req in data['requires']:
        packages[req]['required_by'].append(pkg)


print json.dumps(packages, indent=4)