is it possible to spit out help as default argument when nothing is passed? [closed]

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.

---

This question appears to be off-topic because it lacks sufficient information to diagnose the problem. Describe your problem in more detail or include a minimal example in the question itself.

Closed 8 years ago.

Improve this question

In python's argparse, is it possible to spit out help as default argument when nothing is passed or if some Argparse Exception occurs?

Answer 1

If having zero arguments should trigger the help message, that implies that at least one of your options isn't really optional. Make sure you have at least one positional argument (i.e., one whose name is not prefixed with "--") defined:

p = argparse.ArgumentParser()
p.add_argument("foo", help="Required argument")

Then, if your script isn't called with the argument for foo, the usage message should be triggered.

Answer 2

The parser uses sys.argv[0] for the default prog value, and sys.argv[1:] as input to parse_args. You too can access, and even modify, that array.

import argparse
import sys

parser = argparse.ArgumentParser....
parser.add_argument...

if not sys.argv[1:]:
    # parser.print_help(); parser.exit()
    # or
    # parser.parse_args(['-h'])
    # or
    sys.argv.append('-h')

args = parser.parse_args()

# your code to use args