get usernames on a subreddit bot

getusers.py

import praw
from sets import Set

reddit = praw.Reddit()
submissions = reddit.subreddit

users = Set()
for submission in reddit.subreddit('datasets').new(limit=1000):
    submission.comments.replace_more(limit=1000)
    for comment in submission.comments.list():
        username = unicode(comment.author).encode('utf8')
        users.add(username)

print(users)

praw.ini

[DEFAULT]
client_id=client id
client_secret=client secret
user_agent=get usernames on a subreddit bot