Identifying the dependency relationship for python

Question

When I do a pip freeze I see large number of Python packages that I didn't explicitly install, e.g.

$ pip freeze
Cheetah==2.4.3
GnuPGInterface==0.3.2
Landscape-Client==11.01
M2Crypto==0.20.1
PAM==0.4.2
PIL==1.1.7
PyYAML==3.09
Twisted-Core==10.2.0
Twisted-Web==10.2.0
(etc.)

Is there a way for me to determine why pip installed these particular dependent packages? In other words, how do I determine the parent package that had these packages as dependencies?

For example, I might want to use Twisted and I don't want to depend on a package until I know more about not accidentally uninstalling it or upgrading it.

Answer 1

I wrote a quick script to solve this problem. The following script will display the parent (dependant) package(s) for any given package. This way you can be sure it is safe to upgrade or install any particular package. It can be used as follows: dependants.py PACKAGENAME

#!/usr/bin/python3
# -*- coding: utf-8 -*-

"""Find dependants of a Python package"""

import logging
import pip
import pkg_resources
import sys

__program__ = 'dependants.py'


def get_dependants(target_name):
    for package in pip.get_installed_distributions():
        for requirement_package in package.requires():
            requirement_name = requirement_package.project_name
            if requirement_name == target_name:
                package_name = package.project_name
                yield package_name


# configure logging
logging.basicConfig(format='%(levelname)s: %(message)s',
                    level=logging.INFO)

try:
    target_name = sys.argv[1]
except IndexError:
    logging.error("missing package name")
    sys.exit(1)

try:
    pkg_resources.get_distribution(target_name)
except pkg_resources.DistributionNotFound:
    logging.error("'%s' is not a valid package", target_name)
    sys.exit(1)

print(list(get_dependants(target_name)))