batch.py

#!/usr/bin/env python

import os

users = [filename for filename in os.listdir('/var/cpanel/users') if os.path.isfile(filename)]
batches = ['server8.flaunt7.com', 'server9.flaunt7.com', 'server10.flaunt7.com']

def chunks(lst, n):
    for i in range(0, len(lst), n):
        yield lst[i:i+n]

chunked_users = chunks(users, len(batches))
for i, userlist in enumurate(chunked_users):
    with open(batches[i], 'w') as f:
        f.write('\n'.join(userlist))