from datetime import datetime


def create_identifier(hint: str = '') -> str:
    """
    Can be used to create unique names for files by exploiting the uniqueness of the current date.
    Be aware that if two identifiers are created during the same second they are equal!
    Follows the form YYYY_MM_DD__hh_mm_ss.

    :return: YYYY_MM_DD__hh_mm_ss_{hint}
    """
    now = datetime.now()
    dt_string = now.strftime("%Y_%m_%d__%H_%M_%S")
    return f"{dt_string}_{hint}" if hint else dt_string