Issue with function to customize argparse formatter class

[lucatrv]

I'm reopening here the issue originally opened for mypy, see reply.

I'm using mypy 0.761 with Python 3.8.2 on Windows.

The suggested way to customize the argparse formatter class to control text width is to use a lambda function, as follows:

formatter = lambda prog: argparse.HelpFormatter(prog, width=100)
parser = argparse.ArgumentParser(description=dummy_text, formatter_class=formatter)

but with that code mypy emits the following error:

541: error: Argument "formatter_class" to "ArgumentParser" has incompatible type "Callable[[Any], RawDescriptionHelpFormatter]"; expected "Type[HelpFormatter]"

I could not find any workaround, the only solution is to avoid a function and redefine the formatter class.

See example and discussion.

[srittau]

The formatter_class argument and field should be typed using a callable protocol. Its just called once like this:

        return self.formatter_class(prog=self.prog)