Introduction

A reminder of how to receive a datetime.date type value as an optional argument in python.

Thing you want to do

--Receives a date string (eg 2020-01-01) as an optional argument and converts it to datetime.date type. --Original error message is issued when a malformed character string is passed.

Specify the datetime type with ArgumentParser

For the basic usage of Argparse, Official Tutorial was helpful. In the tutorial, the int type is specified, but this time I want to specify the datetime.date type.

Define a function date_type that converts a date string (eg 2020-01-01) to a date object and specify it in the type of ArgumentParser.

`test.py`


import argparse
import datetime

# str ->date type conversion function
def date_type(date_str):
    return datetime.date.fromisoformat(date_str)

if __name__ == '__main__':
    #Get ArgumentParser
    arg_parser = argparse.ArgumentParser()
    #Definition of date specification options
    arg_parser.add_argument("-d", "--date",
                            help="Date must be in ISO format. For example: 2020-01-01.",
                            type=date_type)
    #Get optional arguments
    args = arg_parser.parse_args()
    date = args.date

    print(date.year,date.month,date.day)

Execution result

>python test.py -d 2020-01-01
2020 1 1

Customize the error message

In the above code, if the optional argument is in a format other than the ISO format date, the following error will be output.

>python test.py -d hoge
usage: mtg.py [-h] [-d DATE]
mtg.py: error: argument -d/--date: invalid date_type value: 'hoge'

I don't like the defined function name date_type being included in the error message, so customize the error content.

Modify the type conversion function date_type as follows.

def date_type(date_str):
    try:
        return datetime.date.fromisoformat(date_str)
    except ValueError as e:
        raise argparse.ArgumentTypeError(str(e) + " Date must be in ISO format. ex. 2020-01-01")

Try-except is raising a new exception.

The type of exception to be processed (ValueError) was actually generated and confirmed.

>>> import datetime
>>> datetime.date.fromisoformat('hoge')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Invalid isoformat string: 'hoge'

Execution result

>python test.py -d hoge
usage: test.py [-h] [-d DATE]
test.py: error: argument -d/--date: Invalid isoformat string: 'hoge' Date must be in ISO format. ex. 2020-01-01

in conclusion

At first I googled with python argparser datetime, but I didn't find any Japanese literature because it was too cornered in the jubako, so I made an article.

References

Official Argparser Tutorial: Argparse Tutorial — Python 3.8.2 Documentation

I also referred to @ kzkadc's article: bow: [A brief summary of how to use ArgumentParser --Qiita](https://qiita.com/kzkadc/items/e4fc7bc9c003de1eb6d0#%E5%9E%8B%E6%8C%87%E5%AE%9A%E3%81% 97% E3% 81% 9F% E3% 81% 84)

Official documentation [argparse ---command line options, arguments, subcommand parsers — Python 3 \ .8 \ .2 documentation](https://docs.python.org/ja/3/library/argparse.html# type)

Receive date type (datetime) with ArgumentParser [python]