gistfile1.py

from collections import defaultdict
import praw

reddit = praw.Reddit(client_id='client_id',
                     client_secret='client_secret',
                     user_agent='user_agent',
                     password='password',
                     username='username')

mods_to_subs = defaultdict(list)

subreddits = reddit.subreddits.popular(limit=100)

for subreddit in subreddits:
    try:
        for moderator in subreddit.moderator():
            mods_to_subs[moderator.name].append(subreddit.display_name)
    except Exception as e:
        print(e)
        print(f'Failed to get moderators for /r/{subreddit.display_name}')


for mod, subs in sorted(mods_to_subs.items(), key=lambda x: -len(x[1])):
    print(f"{mod} moderates {len(subs)} subreddits: {subs}\n")