def extract_name_and_id(user_input):
    """Determines if the string user_input is a name or an id.

    :param user_input: (str): input string from user
    :return: (name, id) pair
    """
    name = id = None
    if user_input.lower().startswith('id:'):
        id = user_input[3:]
    else:
        name = user_input
    return name, id