Is support for Union types on the roadmap?

[Matt Sarmiento]

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to Typer but to Click.

Commit to Help

• I commit to help with one of those options 👆

Example Code

import typer
from typing import Union


def main(name: Union[str, int]):
    print(f"Hello {name}")


if __name__ == "__main__":
    typer.run(main)

Description

Typer does not yet support Union types. Running the above snippet yields:

AssertionError: Typer Currently doesn't support Union types

Not sure how much demand there is for this feature, but I'd personally love to have it.

Operating System

macOS

Operating System Details

No response

Typer Version

0.6.1

Python Version

3.10

Additional Context

Typer is amazing. Absolutely in love with it 💖.

[Emma Jane Bonestell]

https://typer.tiangolo.com/tutorial/commands/help/#help-panels-for-cli-parameters
It might be nice to remove Unions from your examples if it's not on the horizon.

[Nash Taylor]

Just wanted to throw some more engagement on this issue. The number of issues around even the simple | None use case (Union syntax for Optional types) seems to be increasing. For my part, I have a growing number of cases in my CLI where I want to use a Union of types (particularly enums), and I've had to resort to str or Any and parse the type inside the command, because of this missing feature. I would really appreciate if this picked up steam soon.

A quick example of what I'm looking to do:

class EnumA(str, enum.Enum):
    A = "A"
    B = "B"

class EnumB(str, enum.Enum):
    C = "C"
    D = "D"

@cli.command()
def my_command(choice: EnumA | EnumB = typer.Argument(..., help="")) -> None:
    typer.echo(f"You chose {choice}")

Currently, I have to fall back on a str annotation and then parse the str into an enum as the first operation of the command. This also means the documentation for the command is lacking clarity on the options, unless I write it out myself in the help.

[Matt Sarmiento]

@ntaylorwss excellent example. much better than the one i gave and, funnily enough, exactly what i'm after as well. cheers!

[Rachael Sexton]

Just wanted to chime in here. The official Mypy docs lean toward using typing.Literal[] syntax for these kinds of cases, and you don't actually need to support typing.Union at all... literals of literals automatically merge the options (like a union).

See the example here from those docs (the AllowedColors example is particularly salient).

Note that supporting literals would solve #76, which has a lot of recent activity, despite a bot marking it closed 😅... I think #669 is a pretty complete PR for this, though @pchanial would have to chime in on whether that PR already supports compound literals already. :)

To demonstrate @ntaylorwss 's example,

OptA = Literal['A']
OptB = Literal['B']

MyOpts = Literal[OptA, OptB]

### or, equivalently, but without needed OptA/B later ###
MyOpts = Literal['A', 'B']

[Pierre Chanial]

I haven't tried compound Literals, but that's something I could look at if @tiangolo is willing to add Literal handling on the roadmap.

[Christian Kokott]

+1 Would love to see Literal handling as well.

RuntimeError: Type not yet supported: typing.Literal

[Raphael Krupinski]

Use case for a Union: I'd like my program to accept URL (custom type) or Path as a parameter
source: Path | MyUrl