python click subcommand unified error handling

Question

In the case where there are command groups and every sub-command may raise exceptions, how can I handle them all together in one place?

Given the example below:

import click


@click.group()
def cli():
    pass

@cli.command()
def foo():
    pass

if __name__ == '__main__':
    cli()

Both cli and foo may raise. I know that one possible solution is to place try-except around cli() in the if clause. But that does not work when you distribute a package. In setup.py, you have to specify an entry point (in this case, cli). The if clause will not be executed.

Kingsly

Answer 1

You can create a custom click.Group by inheriting from same. The custom group can be used by passing it as the cls parameter to the click.group() decorator. If you override the __call__ method, you can insert an exception handler like:

Code:

class CatchAllExceptions(click.Group):

    def __call__(self, *args, **kwargs):
        try:
            return self.main(*args, **kwargs)
        except Exception as exc:
            click.echo('We found %s' % exc)

Test Code:

import click

@click.group(cls=CatchAllExceptions)
def cli():
    pass

@cli.command()
def foo():
    raise Exception('an exception!')

if __name__ == '__main__':
    cli('foo'.split())

Results:

We found an exception!

Neomaneomah

This doesn't work when attempting to capture the exception in a unit test with the CliRunner. Invoking the custom group as follows: ``` runner = CliRunner() result = runner.invoke(cli, 'foo') print(result)` ``` prints: "an exception!" – Scientist