Using the same option multiple times in Python's argparse

This is simple; just add both action='append' and nargs='*' (or '+').

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-i', action='append', nargs='+')
args = parser.parse_args()

Then when you run it, you get

In [32]: run test.py -i input1_url input1_name input1_other_var -i input2_url i
...: nput2_name input2_other_var -i input3_url input3_name

In [33]: args.i
Out[33]:
[['input1_url', 'input1_name', 'input1_other_var'],
 ['input2_url', 'input2_name', 'input2_other_var'],
 ['input3_url', 'input3_name']]

-i should be configured to accept 3 arguments and to use the append action.

>>> p = argparse.ArgumentParser()
>>> p.add_argument("-i", nargs=3, action='append')
_AppendAction(...)
>>> p.parse_args("-i a b c -i d e f -i g h i".split())
Namespace(i=[['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i']])

To handle an optional value, you might try using a simple custom type. In this case, the argument to -i is a single comma-delimited string, with the number of splits limited to 2. You would need to post-process the values to ensure there are at least two values specified.

>>> p.add_argument("-i", type=lambda x: x.split(",", 2), action='append')
>>> print p.parse_args("-i a,b,c -i d,e -i g,h,i,j".split())
Namespace(i=[['a', 'b', 'c'], ['d', 'e'], ['g', 'h', 'i,j']])

For more control, define a custom action. This one extends the built-in _AppendAction (used by action='append'), but just does some range checking on the number of arguments given to -i.

class TwoOrThree(argparse._AppendAction):
    def __call__(self, parser, namespace, values, option_string=None):
        if not (2 <= len(values) <= 3):
            raise argparse.ArgumentError(self, "%s takes 2 or 3 values, %d given" % (option_string, len(values)))
        super(TwoOrThree, self).__call__(parser, namespace, values, option_string)

p.add_argument("-i", nargs='+', action=TwoOrThree)

If you use action='append' in add_argument() then you will get arguments in list(s) within a list every time you add the option.

As you liked:

[
   ["input1_url", "input1_name", "input1_other"],
   ["input2_url", "input2_name", "input2_other"],
   ["input3_url", "input3_name"]
]

But if anyone wants those arguments in the same list[], then use action='extend' instead of action='append' in your code. This will give you those arguments in a single list.

[
  "input1_url", 
  "input1_name", 
  "input1_other", 
  "input2_url", 
  "input2_name", 
  "input2_other", 
  "input3_url", 
  "input3_name"
]

I used combination of nargs=1 and action="append" for optional argument and got what I wanted

#!/usr/bin/env python3
"""Argparse test"""
from typing import List
import argparse
import sys
import textwrap
if __name__ == "__main__":
    descr = textwrap.dedent(
        """\
        Demonstrate multiple optional attts
    """
    )
    usage = textwrap.dedent(
        """\
    test.py [-d] [-s val] file file
    """
    )
    parser = argparse.ArgumentParser(
        prog="test.py",
        description=descr,
        usage=usage,
        formatter_class=argparse.RawTextHelpFormatter,
    )
    parser.add_argument("-d", "--debug", action="store_true", help="set debug output")
    parser.add_argument("-s", "--skip", nargs = 1, action="append", help="skip")
    parser.add_argument("files", nargs=2, help="files")
    args = parser.parse_args()
    skip_list: List[str] = []
    # Note: args.skip is a list of lists
    if args.skip is not None:
        for inner_list in args.skip:
            for val in inner_list:
                skip_list.append(val)
    print(f"debug={args.debug}")
    print(f"skip-list={skip_list}")
    print(f"files={args.files}")
    sys.exit()

It works as expected

>./test.py file_a file_b
debug=False
skip-list=[]
files=['file_a', 'file_b']
~/python_test
> ./test.py -d -s a -s b file_a file_b
debug=True
skip-list=['a', 'b']
files=['file_a', 'file_b']