Improve typehints for singular_noun

[zmievsa]

Please note that I am only fixing the problem that I personally encountered. If this pattern of "value or False" is more common in the library -- we'd need to fix those cases as well :)

[jaraco]

What is the problem you encountered?

[zmievsa]

@jaraco Let's say you want to get a singular version of the word but you don't know whether the word is already singular.

import inflect

p = inflect.engine()

def get_singular(word: str) -> str:
    new_word = p.singular_noun(word)
    if new_word is False:
        return word
    return new_word

At this point any adequate type checker will tell you that you can't return new_word because its type is str | Literal[True] which makes sense because we have only checked that it's False and your type hints indicate that it can return True.

Essentially I am just making the type hints here more specific to make sure that type checkers are not angry and for correctness.

[jaraco]

Why 3.7.2? I looked up the changelog, but it directs to the git history for versions prior to 4.0. I don't want to add a specific version unless there was a specific reason for the minimum pertinent to this project.

[zmievsa]

I believe that Literal wasn't added until this version. Any version can be picked as long as it's after this one.

[jaraco]

Okay. I did confirm the introduction of Literal appears in the changelog between 3.6.6 and 3.7.4. There's no tag for 3.7.2, unfortunately, leaving it difficult to confirm that the feature was added in that version. Since we're not certain and because those releases are already years old and because this project is likely to depend on features later than that release, I'll just leave it unspecified (when I merge).