Custom date/datetime type validators for python's argparse module

argparse_date_datetime_custom_types.py

def valid_date_type(arg_date_str):
    """custom argparse *date* type for user dates values given from the command line"""
    try:
        return datetime.datetime.strptime(arg_date_str, "%Y-%m-%d")
    except ValueError:
        msg = "Given Date ({0}) not valid! Expected format, YYYY-MM-DD!".format(arg_date_str)
        raise argparse.ArgumentTypeError(msg)
        
def valid_datetime_type(arg_datetime_str):
    """custom argparse type for user datetime values given from the command line"""
    try:
        return datetime.datetime.strptime(arg_datetime_str, "%Y-%m-%d %H:%M")
    except ValueError:
        msg = "Given Datetime ({0}) not valid! Expected format, 'YYYY-MM-DD HH:mm'!".format(arg_datetime_str)
        raise argparse.ArgumentTypeError(msg)        
        
        
if __name__ == '__main__':
    import argparse
    parser = argparse.ArgumentParser(description='Example of custom type usage')
    parser.add_argument('-s', '--start-datetime',
                        dest='start_datetime',
                        type=valid_datetime_type,
                        default=None,
                        required=True,
                        help='start datetime in format "YYYY-MM-DD HH:mm"')
    args = parser.parse_args()
    start_datetime_object = args.start_datetime
    print(start_datetime_object)

From python 3.7 you can use following two options
For date:

parser.add_argument('--date',  type=datetime.date.fromisoformat, help='ISO format - YYYY-MM-DD')
parser.add_argument('--date',  type=datetime.datetime.fromisoformat, help='ISOformat - YYYY-MM-DD:HH:mm:ss')