def checkAlias(alias):
    """
    Check an alias for invalid characters; raise AXError if any are
    found.  Return None if the alias is valid.
    """
    if ',' in alias:
        raise AXError("Alias %r must not contain comma" % (alias,))
    if alias in '.':
        raise AXError("Alias %r must not contain period" % (alias,))
dataset/ETHPy150Open necaris/python3-openid/openid/extensions/ax.py/checkAlias/swapped operands of `in`