Passing integer lists to python

Question

I want to pass 2 lists of integers as input to a python program.

For e.g, (from command line)

python test.py --a 1 2 3 4 5 -b 1 2  

Answer 1

Just adding this one for completeness. I was surprised that I didn't see this approach.

from argparse import Action, ArgumentParser


class CommaSeparatedListAction(Action):
    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest, values.split(','))


parser = ArgumentParser()
parser.add_argument('-l', action=CommaSeparatedListAction)
print(parser.parse_args('-l a,b,c,d'.split()))

# Namespace(l=['a', 'b', 'c', 'd'])

This just a basic example, but you can also add validation or transform values in someway such as coercing them to uppercase.

from argparse import Action, ArgumentParser


class UppercaseLetterCommaSeparatedListAction(Action):
    def __call__(self, parser, namespace, values, option_string=None):
        letters = values.split(',')
        for l in letters:
            self._validate_letter(parser, l)
        setattr(
            namespace,
            self.dest,
            list(map(lambda v: v.upper(), letters))
        )

    def _validate_letter(self, parser, letter):
        if len(letter) > 1 or not letter.isalpha():
            parser.error('l must be a comma separated list of letters')


parser = ArgumentParser()
parser.add_argument('-l', action=UppercaseLetterCommaSeparatedListAction)
print(parser.parse_args('-l a,b,c,d'.split()))

# Namespace(l=['A', 'B', 'C', 'D'])

parser = ArgumentParser()
parser.add_argument('-l', action=UppercaseLetterCommaSeparatedListAction)
print(parser.parse_args('-l a,bb,c,d'.split()))

# usage: list.py [-h] [-l L]
# list.py: error: l must be a comma separated list of letters

parser = ArgumentParser()
parser.add_argument('-l', action=UppercaseLetterCommaSeparatedListAction)
print(parser.parse_args('-l a,1,c,d'.split()))

# usage: list.py [-h] [-l L]
# list.py: error: l must be a comma separated list of letters