bug: click_type with List[CustomType] adds a nested list

[FredrikM97]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question 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 tutorials 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
import click
import json
from typing import List

class Curfew:
    def __init__(self, enabled: bool, lock_time: str, unlock_time: str):
        self.enabled = enabled
        self.lock_time = lock_time
        self.unlock_time = unlock_time
    def __repr__(self):
        return f"Curfew(enabled={self.enabled}, lock_time={self.lock_time}, unlock_time={self.unlock_time})"

class CurfewParamType(click.ParamType):
    name = "curfew"
    def convert(self, value, param, ctx):
        print("Testing")
        data = json.loads(value)
        return [Curfew(**item) for item in data]

app = typer.Typer()

@app.command()
def test_curfew(
    state: List[Curfew] = typer.Option(
        None,
        "--state",
        "-s",
        help="Set new curfew times (omit to show current).",
        click_type=CurfewParamType(),
    )
):
    typer.echo(f"state: {state}")


if __name__ == "__main__":
    app()

Description

• I create a custom type and then create a ParamType to convert from json string to list of objects
• Use this input:'[{"enabled": true, "lock_time": "08:00", "unlock_time": "18:00"}]'
• Expected return: [Curfew(enabled=True, lock_time=08:00, unlock_time=18:00)].
• Actual return: [[Curfew(enabled=True, lock_time=08:00, unlock_time=18:00)]]
• After changing state: List[Curfew] = typer.Option( to state: Curfew = typer.Option( the expected return is given
• I expect that the type hint should not affect the response of the typer.Option and not wrap an extra list around the response.

Try the code with:

• python3 file.py --state '[{"enabled": true, "lock_time": "08:00", "unlock_time": "18:00"}]'

Operating System

macOS

Operating System Details

Running in docker

Typer Version

0.19.2

Python Version

Python 3.13.7

Additional Context

No response