Bug report

If you add an optional argument to a parser with argparse containing dashes,
those are converted to _ automatically in the resulting Namespace object.

But if you add a positional argument containing a -, this is not converted and the resulting error message suggests the argument name containing the - instead of the _. Which is of course not possible (without getattr), because it's not a valid variable name in Python.

This behaviour is misleading and undocumented and I'd suggest to convert - to _ in positional arguments too.

Reproduction code:

import argparse

parser = argparse.ArgumentParser("example")

parser.add_argument("foo-bar", type=str)

args = parser.parse_args()

print("getattr", getattr(args, "foo-bar"))

print("- replaced by _", args.foo_bar)

Results in:

$ python3 main.py abc
getattr aoe
Traceback (most recent call last):
  File "/tmp/main.py", line 11, in <module>
    print("- replaced by _", args.foo_bar)
AttributeError: 'Namespace' object has no attribute 'foo_bar'. Did you mean: 'foo-bar'?

Compounding this issue is the fact, that you are prevented from using the dest option on add_argument to overwrite the name in the Namespace.

Your environment

• CPython versions tested on: Python 3.10.5
• Operating system and architecture: Linux