Support Python 3.10 optional union types

[potatoeggy]

In Python 3.10+, recognise that SomeType | None is analogous to Optional[SomeType]. AFAIK, this shouldn't break anything pre-3.10 because it checks things via duck typing. Resolves #371, resolves #348.

Instead of:

from typing import Optional

app = typer.Typer()

@app.command()
def command(option: Optional[str] = None, test: Optional[int] = typer.Option(None)):
  ...

Allow:

app = typer.Typer()

@app.command()
def command(option: str | None = None, test: int | None = typer.Option(None)):
  ...

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[HansAarneLiblik]

Any advancements on this ?

[potatoeggy]

cc @tiangolo?

[ArVar]

I would appriciate this merge as well. :-)

[NiklasRosenstein]

May I suggest using the typeapi module to add support for new-style type hints in Python versions before 3.10? It can evaluate forward references that make use of

• PEP 585 - Type Hinting Generics In Standard Collections
• PEP 604 - Allow writing union types as X | Y

I'm currently using it in my own Typer wrapper terracomp_typer to convert annotations before they are passed to Typer. All it does is run a function being passed to Typer through this beforehand:

from inspect import signature
from typeapi import get_annotations

def _evaluate_type_hints(func: Callable[..., Any]) -> Callable[..., Any]:
    annotations = get_annotations(func)
    sig = signature(func)
    sig = sig.replace(
        parameters=[p.replace(annotation=annotations.get(p.name, p.empty)) for p in sig.parameters.values()],
        return_annotation=annotations.get("return", Signature.empty),
    )
    func.__signature__ = sig  # type: ignore[attr-defined]
    func.__annotations__ = annotations
    return func

This will evaluate string annotations and forward references, most notably it can turn "str | None" to Optional[str] and "list[int]" to List[int].

It could also replace Typer's currently, if I may say so, seemingly brittle, implementation of introspecting type hints. The typeapi module provides an API for type hints so that Typer could focus on interpreting the actual type hints. I say "brittle" because the code currently tries to do two things at the same time, i.e. trying to work with the unstable and inconsistent typing API while also trying to make sense of the actual typing information.

Disclaimer: I'm the author of typeapi.

Edit: terracomp-typer started as a utility library for another tool; but I've found it useful in many of my projects now which is why I migrated it to typer-builder on PyPI.

[kudlatyamroth]

can we get this merged?

[johnthagen]

@tiangolo Would you have time to review this PR? ❤️

[realstealthninja]

LGTM

[potatoeggy]

Superceded by #676, which is a more elegant solution.