def get_sanitised_resp_msg(exp):
    """Get the sanitise response messages from a calendar response

    Returns the sanitised message, with any character not in the whitelist replaced by '_'
    """
    WHITELIST = (
        b'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789#-.,; '
        )
    raw_msg = bytearray(exp.read(160))
    for i in range(len(raw_msg)):
        if raw_msg[i] not in WHITELIST:
            raw_msg[i] = ord('_')
    return raw_msg.decode()
