condaroots.py

import sys
import json
import os
import collections

pkgs = {}
for f in os.listdir(os.path.join(sys.prefix, 'conda-meta')):
    path = os.path.join(sys.prefix, 'conda-meta', f)
    if path.endswith('.json'):
        with open(path) as fp:
            data = json.load(fp)
        pkgs[data['name']] = [i.split()[0] for i in data['depends']]

revpkgs = collections.defaultdict(list)

for n in pkgs:
    revpkgs[n] = []
for n,d in pkgs.items():
    for p in d:
        revpkgs[p].append(n)

# packages that don't depend on anything else
leaves = sorted([n for n,d in pkgs.items() if len(d)==0])
print('Packages not depending on any others: %s'%' '.join(leaves))

# packages that nobody else depends on (minimal set needed to create environment)
roots = sorted([n for n,d in revpkgs.items() if len(d)==0])
print('Package roots, no others depend on: %s'%' '.join(roots))