argparse: make one argument default when no arguments are called

Question

What's the best way to set a group argument as the default when no arguments are called.

parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument("--a", action="store_true") #call when no arguments are provided
group.add_argument("--b", action="store_true")
group.add_argument("--c", action="store_true")

Let's call my program argparse_ex.py. I want argparse.py (with no arguments) and argparse.py --a to return the same output.

hpaulj · Accepted Answer · 2016-08-16 19:53:58Z

1

I would just add a simple test after parsing

if not any([args.a, args.b, args.c]):
   args.a=True

This is simpler than any attempt to make parse_args to do this. The parser will parse all arguments independently - and in any order. So you really can't tell until the parsing is all done whether any of the options has been selected or not.

answered Aug 16, 2016 at 19:53

hpaulj

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