How to create argument of type "list of pairs" with argparse?

Question

I need to let the end user of my python script types something like:

script.py -sizes <2,2> <3,3> <6,6>

where each element of the -sizes option is a pair of two positive integers. How can I achieve this with argparse ?

Answer 1

Define a custom type:

def pair(arg):
    # For simplity, assume arg is a pair of integers
    # separated by a comma. If you want to do more
    # validation, raise argparse.ArgumentError if you
    # encounter a problem.
    return [int(x) for x in arg.split(',')]

then use this as the type for a regular argument:

p.add_argument('--sizes', type=pair, nargs='+')

Then

>>> p.parse_args('--sizes 1,3 4,6'.split())
Namespace(sizes=[[1, 3], [4, 6]])