[QUESTION] How to handle mutually exclusive options

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Description

I often find myself making mutually exclusive options. I’m used to argparse, which has nice support for that. What is the best way to do this in Typer?

I.e. how to (best) achieve something like this argparse code:

parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument("--opt-A, action="store_true")
group.add_argument("--opt-B, action="store_true")

I found several mentions of ways to do it with Click, but none that were “built-in”, nor I’m I clear on how I’d use that with Typer.

Any help would be much appreciated. I really like the feel of Typer!

Issue Analytics

State:
Created 3 years ago
Reactions:33
Comments:17 (3 by maintainers)

Top GitHub Comments

12reactions

OdinTech3commented, Aug 14, 2021

Hey my fellow Pythonistas, I often comeback to this issue from time to time because it’s still a problem for me so I took @daddycocoaman answer and came up with this:

import typer

app = typer.Typer()

def MutuallyExclusiveGroup(size=2):
    group = set()
    def callback(ctx: typer.Context, param: typer.CallbackParam, value: str):
        # Add cli option to group if it was called with a value
        if value is not None and param.name not in group:
            group.add(param.name)
        if len(group) > size-1:
            raise typer.BadParameter(f"{param.name} is mutually exclusive with {group.pop()}")
        return value
    return callback

exclusivity_callback = MutuallyExclusiveGroup()

@app.command()
def main(
        optA: str = typer.Option(None, callback=exclusivity_callback),
        optB: int = typer.Option(None, callback=exclusivity_callback)
    ):
    typer.echo(f"Option A is {optA} and Option B is {optB}")


if __name__ == "__main__":
    app()

Using the function MutuallyExclusiveGroup I return another function within a closure where there is state, a set called group as typer invokes the callbacks the logic will check if more than one option I have added the exclusivity_callback was called in the command line and raises an exception.

$ python cli.py --optb 3 --opta wow
Usage: cli.py [OPTIONS]

Error: Invalid value for '--opta': optA is mutually exclusive with optA

$ python cli.py --optb 3
Option A is None and Option B is 3

$ python cli.py --opta 3 --optb wow
Usage: cli.py [OPTIONS]
Try 'cli.py --help' for help.

Error: Invalid value for '--optb': wow is not a valid integer

$ python cli.py --opta wow --optb 3
Usage: cli.py [OPTIONS]

Error: Invalid value for '--optb': optB is mutually exclusive with optA

$ python cli.py --opta wow
Option A is wow and Option B is None

If you need to ensure at least one of the options are passed to the command line then manually check it in the body of your function for the command like so

@app.command()
def main(
        optA: str = typer.Option(None, callback=exclusivity_callback),
        optB: int = typer.Option(None, callback=exclusivity_callback)
    ):

    if not any([optA, optB]):
        raise typer.BadParameter("At least optA or optB is required.")
        
    typer.echo(f"Option A is {optA} and Option B is {optB}")

5reactions

robinbowescommented, Mar 17, 2022

Just adding another “I’d like to see this too” comment.