import re


def _is_token(token_s):
    """
    Given a string, returns True if the string contains a Bookalope token, or
    False otherwise. A Bookalope token contains 32 lower-case hex characters,
    i.e. must match the regular expression [0-9a-f]{32}.

    :param str token_s: The string to be checked.

    :returns bool: True if the string is a valid Bookalope token, False otherwise.
    """
    return re.match(r"^[0-9a-f]{32}$", token_s or "") is not None