(host)
return (user if delim else None), host
splituser('user[:passwd]@host[:port]') --> 'user[:passwd]', 'host[:port]'.
splituser('user[:passwd]
splituser ( user [ : passwd ]
def _splituser(host):
    """splituser('user[:passwd]@host[:port]') --> 'user[:passwd]', 'host[:port]'."""
    user, delim, host = host.rpartition('@')
    return (user if delim else None), host
def _splituser ( host ) : user , delim , host = host . rpartition ( '@' ) return ( user if delim else None ) , host