CODEWITHSUNDEEP
pythonargparse
Sohaib
Sohaib

Reputation: 4694

Specify date format for Python argparse input arguments

I have a Python script that requires some command line inputs and I am using argparse for parsing them. I found the documentation a bit confusing and couldn't find a way to check for a format in the input parameters. What I mean by checking format is explained with this example script:

parser.add_argument('-s', "--startdate", help="The Start Date - format YYYY-MM-DD ", required=True)
parser.add_argument('-e', "--enddate", help="The End Date format YYYY-MM-DD (Inclusive)", required=True)
parser.add_argument('-a', "--accountid", type=int, help='Account ID for the account for which data is required (Default: 570)')
parser.add_argument('-o', "--outputpath", help='Directory where output needs to be stored (Default: ' + os.path.dirname(os.path.abspath(__file__)))

I need to check for option -s and -e that the input by the user is in the format YYYY-MM-DD. Is there an option in argparse that I do not know of which accomplishes this?

Upvotes: 159

Views: 76626

Answers (3)

jonrsharpe
jonrsharpe

Reputation: 122032

Per the documentation:

The type keyword argument of add_argument() allows any necessary type-checking and type conversions to be performed ... The argument to type can be any callable that accepts a single string.

You could do something like:

import argparse
import datetime


def valid_date(s: str) -> datetime.datetime:
    try:
        return datetime.datetime.strptime(s, "%Y-%m-%d")
    except ValueError:
        raise argparse.ArgumentTypeError(f"not a valid date: {s!r}")

Then use that as type:

parser.add_argument(
    "-s", 
    "--startdate", 
    help="The Start Date - format YYYY-MM-DD", 
    required=True, 
    type=valid_date
)

If the user supplies an invalid value, the feedback will look like:

error: argument -s/--startdate: not a valid date: 'foo'

Upvotes: 295

Evan V
Evan V

Reputation: 1350

Just to add on to the answer above, you can use a lambda function if you want to keep it to a one-liner. For example:

parser.add_argument('--date', type=lambda d: datetime.strptime(d, '%Y-%m-%d'))

If the user supplies an invalid value, the feedback will look like:

error: argument -e/--enddate: invalid <lambda> value: 'foo'

Upvotes: 84

Michał G&#243;rny
Michał G&#243;rny

Reputation: 19243

In Python 3.7 you can use the standard .fromisoformat class method instead of reinventing the wheel for ISO-8601 compliant dates, e.g.:

import datetime

parser.add_argument('-s', "--startdate",
    help="The Start Date - format YYYY-MM-DD",
    required=True,
    type=datetime.date.fromisoformat)
parser.add_argument('-e', "--enddate",
    help="The End Date format YYYY-MM-DD (Inclusive)",
    required=True,
    type=datetime.date.fromisoformat)

If the user supplies an invalid valid, the feedback will look like:

error: argument -e/--enddate: invalid fromisoformat value: 'foo'

Upvotes: 76

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