def ban(email):
    """Ban an email address from subscribing to a mailing list.

        When an email address is banned, it will not be allowed to subscribe
        to the mailing list.  This does not affect any email address that may
        already be subscribed to a mailing list.

        It is also possible to add a 'ban pattern' whereby all email addresses
        matching a Python regular expression can be banned.  This is
        accomplished by using a `^` as the first character in `email`.

        When an email address is already banned.  However, it is possible to
        extend a ban for a specific mailing list into a global ban; both bans
        would be in place and they can be removed individually.

        :param email: The text email address being banned or, if the string
            starts with a caret (^), the email address pattern to ban.
        :type email: str
        """
