import six


def convert_id36_to_numeric_id(id36):
    """Convert strings representing base36 numbers into an integer."""
    if not isinstance(id36, six.string_types) or id36.count("_") > 0:
        raise ValueError("must supply base36 string, not fullname (e.g. use "
                         "xxxxx, not t3_xxxxx)")
    return int(id36, 36)