[FEATURE] Literal type support

[alippai]

Support for the literal type (python 3.8 or via typing_extensions) would be nice. Eg.

def get_list(output: Literal["raw", "json", "yaml"] = "raw"):
  if output == "json":
    typer.echo(json.dumps([1, 2, 3]))

The only workarounds (using string or multiple bool flags + validating input) are ugly now.

[tiangolo]

I think you can solve it with an enum.

Here are the docs: https://typer.tiangolo.com/tutorial/parameter-types/enum/

[alippai]

This could work indeed

[tiangolo]

Great! If that answers your question you can then close the issue.

[github-actions]

Assuming the original issue was solved, it will be automatically closed now. But feel free to add more comments or create new issues.

[Aran-Fey]

I don't get why this is closed. Does this mean you won't be adding support for typing.Literal? Or did the bot mess up?

This sounds pretty useful to me.

[arogozhnikov]

Literal is pretty useful, and supported by pydantic for a while.

Certainly vote for adding support. There is a pretty well-written PR too #174.

If that one isn't satisfactory, @tiangolo please state this, because reason for not supporting is unclear

[f4hy]

While things could be rewritten as an enum, it does not play nice with existing typed code which uses typing.Literal to define a set of allowed values. I hope we can revisit this.

[kimothy]

I agree as @f4hy as well. In many cases typing.Literal is a much more elegant solution then using enum.Enum.

[lainisourgod]

@tiangolo I have a case similar to @f4hy. In my ML project I use smth like TargetType = typing.Literal["age", "income", "gender"] to specify which targets I train model for, and use it in dicts ({"age": 40, "income": 11}), keys in exported json-s, and as argument types to functions so I can be sure I won't use unspecified target in my code.

I don't wanna rewrite everything else in enum style, it will be tedious and harder to use.

[woutervh]

Can we reopen this ticket?

Silly bots closing open tickets because they misinterpret a sentence is quite annoying.