Python argument parser list of list or tuple of tuples

Question

I'm trying to use argument parser to parse a 3D coordinate so I can use

--cord 1,2,3 2,4,6 3,6,9

and get

((1,2,3),(2,4,6),(3,6,9))

My attempt is

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--cord', help="Coordinate", dest="cord", type=tuple, nargs=3)
args = parser.parse_args(["--cord","1,2,3","2,4,6","3,6,9"])

vars(args) 
{'cord': [('1', ',', '2', ',', '3'),
  ('2', ',', '4', ',', '6'),
  ('3', ',', '6', ',', '9')]}

What would the replacement of the comma be?

+1 for showing your attempt and for using the standard lib instead of reinventing — mechanical_meat, Apr 02 '12 at 15:33

score 78 · Accepted Answer · answered Apr 02 '12 at 15:28

78

You can add your own type. This also allows for additional validations, for example:

def coords(s):
    try:
        x, y, z = map(int, s.split(','))
        return x, y, z
    except:
        raise argparse.ArgumentTypeError("Coordinates must be x,y,z")


parser.add_argument('--cord', help="Coordinate", dest="cord", type=coords, nargs=3)

answered Apr 02 '12 at 15:28

georg

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1

+1 Thanks! Have changed the raise to a TypeError. Thanks for the answer! – joedborg Apr 02 '12 at 16:20
2

since this case is a `3D` coordinate `nargs=3` is obvious, but if your case doesn't require a fixed number of tuples, you can use `nargs='+'` – Juan-Kabbali May 19 '21 at 15:01

brodegon · Answer 2 · 2021-10-04T09:54:57.807

For my problem, I had to have a more general approach, not linked to the number of inputs.

Starting from the great answer by georg, I solved my problem as follows

# additional type
def coords(s):
    seps = r'[ ;.]'
    try:
        situp = []
        for si in re.split(seps, s):
            situp.append(tuple(map(int, si.split(','))))
        return situp
    except:
        raise argparse.ArgumentTypeError("Coordinates must be given divided by commas and space, dot, or semicolon e.g.: 'x,y k,l,m'")

With this, an input like 1,2 3,4,5 will be turned in a list of tuples like [(1,2), (3,4,5)]

EDIT: It might be that the for loop is not optimal, but I wrote it to avoid the use of nargs

EDIT 2:

to have a list of list, one should change

the line situp.append(tuple(map(int, si.split(','))))

with situp.append(list(map(int, si.split(','))))
to have a tuple of uples one can just change the return with

return tuple(situp)

Python argument parser list of list or tuple of tuples

2 Answers2