Converting Excel date serial numbers to Python datetime format

def date_serial_number(serial_number: int) -> datetime:
    """
    Convert an Excel serial number to a Python datetime object
    :param serial_number: the date serial number
    :return: a datetime object
    """
    # Excel stores dates as "number of days since 1900"
    import datetime as dt

    delta = dt.datetime(1899, 12, 30) + dt.timedelta(days=serial_number)
    return delta