How do I constrain my python script to only accepting one argument? (argparse)

Question

I would like a script that has (for example) three arguments:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--a",help="Argument a")
parser.add_argument("--b",help="Argument b")
parser.add_argument("--c",help="Argument c")
args= parser.parse_args()

But make it so that it is only possible to specify only either 'a','b', or 'c' at any give time e.g. you can specify 'a' but not 'b' or 'c' Is this possible and how would I achieve it?

Answer 1

argpase lets you specify this using the add_mutually_exclusive_group() method.

import argparse
parser = argparse.ArgumentParser()
g = parser.add_mutually_exclusive_group()
g.add_argument("--a",help="Argument a")
g.add_argument("--b",help="Argument b")
g.add_argument("--c",help="Argument c")
args= parser.parse_args()

Answer 2

Use the add_mutually_exclusive_group() mentioned above to check this on the argparse level already.

If you like to have more control about error message and the like, you can of course check the results later:

if len([x for x in args.a, args.b, args.c if x is not None]) > 1:
  raise Exception("Not allowed!")