Derive next available username

derive_username.py

# from simonw's code to djangopeople.net
import re
notalpha_re = re.compile('[^a-zA-Z0-9]')

def derive_username(nickname):
    nickname = notalpha_re.sub('', nickname)
    if not nickname:
        return ''
    base_nickname = nickname
    to_add = 1
    while True:
        try:
            DjangoPerson.objects.get(user__username = nickname)
        except DjangoPerson.DoesNotExist:
            break
        nickname = base_nickname + str(to_add)
        to_add += 1
    return nickname