Empty tuple returned for Option instead of expected `None` when no values passed

[Andrew-Sheridan]

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Example Code

import typer
from typing import Optional, List

app = typer.Typer(add_completion=False)


@app.command()
def main(
    foos: Optional[tuple[str]] = typer.Option(None, "--foo"),
    bar: Optional[str] = typer.Option(None, "--bar"),
):
    print(f"{type(foos)=}, {foos=}")
    print(f"{type(bar)=}, {bar=}")


if __name__ == "__main__":
    app()

Description

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.

❯ python issue.py --help
Usage: issue.py [OPTIONS]

Options:
  --foo TEXT
  --bar TEXT
  --help      Show this message and exit.

Nothing passed causes the returned value for foo to be an empty tuple, it should be None:

❯ python issue.py
type(foos)=<class 'tuple'>, foos=()
type(bar)=<class 'NoneType'>, bar=None

Passing values it returns a tuple of the values

❯ python issue.py --foo Hello --foo World --bar Goodbye
type(foos)=<class 'tuple'>, foos=('Hello', 'World')
type(bar)=<class 'str'>, bar='Goodbye'

Operating System

macOS

Operating System Details

No response

Typer Version

0.4.1

Python Version

3.10.0

Additional Context

https://github.com/tiangolo/typer/issues/127#issuecomment-721710767

[jonasjancarik]

The same thing happens with lists (an empty list is returned instead of None) when you use Optional[List[str]] = typer.Option(None) (as suggested in https://typer.tiangolo.com/tutorial/multiple-values/multiple-options/)

[svlandeg]

Hi, thanks for the report! It looks like this is still an issue. I'll go ahead and merge this issue report with the similar report in https://github.com/tiangolo/typer/issues/170, and close this one to keep the discussion in one thread.