[BUG] Multiple value option gives tuple and not list

[jayqi]

Describe the bug

The standard way to configure an option that expects multiple values is to declare with List, as described in the docs.

However, this provides a tuple of values, and not a list of values, as one would expect based on the type hint declaration. It also contradicts the documentation, which states "You will receive the values as you declared them, as a list of str".

To Reproduce

Steps to reproduce the behavior with a minimum self-contained file.

• Create a file main.py with:

from typing import List
import typer


def my_command(opt: List[str] = ["foo", "bar"]):
    typer.echo(opt)
    typer.echo(type(opt))


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

• Call it with:

python main.py

• It outputs:

('foo', 'bar')
<class 'tuple'>

• Call it with:

python main.py --opt baz

• It outputs:

('baz',)
<class 'tuple'>

Expected behavior

I would expect to get a container of values that is class list as declared.

Environment

• OS: macOS 10.15.4
• Python 3.6.10
• Typer 0.3.0

[ovezovs]

I was able to reproduce this issue. Would this be considered a bug or a documentation issue, @tiangolo? I'd like to work on this.

[ovezovs]

UPDATE: I have discussed this with my MLH mentor and we concluded that it was a bug, however, I am not sure if the bug is in the typing library or Typer itself.

[tiangolo]

Hey @ovezovs ! Thanks!

Yes, I think it would probably make sense to ensure that the value passed is a list in this case, converting it to a list if it is not.

[hellowhistler]

UPDATE: I have discussed this with my MLH mentor and we concluded that it was a bug, however, I am not sure if the bug is in the typing library or Typer itself.

Hi @ovezovs, are you still planning on looking into this (or already working on it)? I encountered this bug in the wild, and if you've changed your mind, I'd be interested in trying to fix it.

[ovezovs]

Hi @ovezovs, are you still planning on looking into this (or already working on it)? I encountered this bug in the wild, and if you've changed your mind, I'd be interested in trying to fix it.

Feel free to take on it.

[Andrew-Sheridan]

As an extra layer to this, if an option is declared as foo: Optional[List[str]] = typer.Option(None) it should provide None if nothing is passed. Currently it is providing (), an empty tuple.

In comparison bar: Optional[str] = typer.Option(None) does provide None when missing, as expected.

Would this be considered the same issue, or should I raise a new one?

[tiangolo]

Thanks for the clear example @jayqi! 🤓 🍰

And thanks for the discussion everyone. ☕

@Andrew-Sheridan, could you please create a new issue with that example?

This was fixed by @hellowhistler in #143

It will be available in the next release, in some hours, Typer version 0.4.2 🎉

[Andrew-Sheridan]

@Andrew-Sheridan, could you please create a new issue with that example?

Created #410 with the example