Clean Username if Email Address

email_to_username.py

def clean_username(un):
    import re

    # clean username
    un = re.sub(r'[^a-zA-Z0-9._]+', '', un)

    # soft truncate
    if len(un) > 30:
        un = un.split('@')[0]  # pray for email address

    # hard truncate
    return un[:30]