Checks if the passed in uid is a valid UID

    :param uid: The uid to check
    :type uid: string
    :return: True if the uid is a valid 32 alphanumeric uid or '0'
    :rtype: bool

def is_uid(uid):
    """Checks if the passed in uid is a valid UID

    :param uid: The uid to check
    :type uid: string
    :return: True if the uid is a valid 32 alphanumeric uid or '0'
    :rtype: bool
    """
    if not isinstance(uid, basestring):
        return False
    if uid != "0" and len(uid) != 32:
        return False
    return True