TypingHintArgSpecGuesser breaks on type alias List

[thorwhalen]

Sorry not to give further details but I had the choice between sending a quick issue or not mentioning it at all.

My script, that uses argh, stopped working when I updated to argh==0.31.0 from argh==0.26.2.

The error

    argh.dispatch_command(populate_pkg_dir)
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/dispatching.py", line 470, in dispatch_command
    set_default_command(parser, function, name_mapping_policy=name_mapping_policy)
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 420, in set_default_command
    inferred_args: List[ParserAddArgumentSpec] = list(
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 183, in infer_argspecs_from_function
    TypingHintArgSpecGuesser.typing_hint_to_arg_spec_params(
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 778, in typing_hint_to_arg_spec_params
    item_type = cls._extract_item_type_from_list_type(first_subtype)
  File "~.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 799, in _extract_item_type_from_list_type
    if args[0] in cls.BASIC_TYPES:
IndexError: tuple index out of range

My guess is that the len(args) == 0 case is not handled properly?

Without looking further, I'd suggest:

 if args and (args[0] in cls.BASIC_TYPES):

instead?

If I have time, I'll look at it further this week and send a PR.

[thorwhalen]

I went ahead and made a PR for this: #217

[neithere]

Minimal example as discussed in the related PR:

• def func(xs: list) — works
• def func(xs: List) — breaks

[thorwhalen]

@neithere : This still breaks for me with argh==0.31.1:

from typing import Optional, List

def func(x: Optional[List] = None):
        return 'hello'

if __name__ == '__main__':
    import argh

    argh.dispatch_command(func)

Note that replacing Optional[List] with Optional[list] or just List works though.

  File "~/tmp/scrap.py", line 9, in <module>
    argh.dispatch_command(func)
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/dispatching.py", line 470, in dispatch_command
    set_default_command(parser, function, name_mapping_policy=name_mapping_policy)
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 420, in set_default_command
    inferred_args: List[ParserAddArgumentSpec] = list(
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 183, in infer_argspecs_from_function
    TypingHintArgSpecGuesser.typing_hint_to_arg_spec_params(
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 778, in typing_hint_to_arg_spec_params
    item_type = cls._extract_item_type_from_list_type(first_subtype)
  File "~/.pyenv/versions/p10/lib/python3.10/site-packages/argh/assembling.py", line 799, in _extract_item_type_from_list_type
    if args[0] in cls.BASIC_TYPES:
IndexError: tuple index out of range

[neithere]

Ahh, you're right. I fixed a more general case but it was not enough.

Will ship the fix with 0.31.2 later today.

BTW, we'll get rid of those aliases (List etc.) when we drop support for Python 3.8 (pretty soon), they are deprecated since Python 3.9, so I'd really try to use Optional[list] or even list | None whenever possible.