How do I parse a date as an argument with argparse?

Im trying to write a python program that I will run at the command line. I'd like the program to take a single input variable. Specifically, I would use a date in the form of 2014-01-28 (yyyy-mm-dd):

e.g. python my_script.py 2014-01-28

It seems argparse might be able to help me but I have found very little documentation regarding the module. Does anyone have experience with something like this?

Solution 1:

There's lots of documentation in the standard library, but generally, something like:

import argparse
import datetime

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

# For testing.  Pass no arguments in production
args = parser.parse_args(['2012-01-12'])
print(args.date) # prints datetime.datetime object

Solution 2:

As of Python 3.7, a (marginally) more convenient option is fromisoformat: https://docs.python.org/3/library/datetime.html#datetime.date.fromisoformat

Using it, you can replace the relevant line in mgilson's code with this:

parser.add_argument('date', type=datetime.date.fromisoformat)

(I would also add a help argument to this invocation of add_argument, and mention that the input should be in ISO format.)