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

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