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Passing an instance of Pathlib.Path to CliRunner.invoke() gets a TypeError #1324

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alexwlchan opened this issue May 27, 2019 · 3 comments
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Passing an instance of Pathlib.Path to CliRunner.invoke() gets a TypeError #1324

alexwlchan opened this issue May 27, 2019 · 3 comments
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good first issue save-for-sprint

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@alexwlchan
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@alexwlchan alexwlchan commented May 27, 2019 •
edited

Consider the following example:

from pathlib import Path

import click
from click.testing import CliRunner


@click.command()
@click.argument("DIRNAME")
def print_directory(dirname):
    print(dirname)


runner = CliRunner()
print(runner.invoke(print_directory, ["example"]))
print(runner.invoke(print_directory, [Path("example")]))

With Python 3.6.4 and click 7.0, this is the output you get:

<Result okay>
<Result TypeError("object of type 'PosixPath' has no len()",)>

This can be easily fixed by wrapping in str(), i.e.,

print(runner.invoke(print_directory, [str(Path("example"))]))

But in general I've got used to the implicit contract (at least in the standard library) that I can use a Path object anywhere I can use a string representation of a path. Since paths are often the arguments to command-line tools, it'd be nice to be able to use a Path object here as well.

Alternatively, raise a more helpful TypeError if you pass a non-string object into invoke() – I spent a while poking around in my code to see where I was calling len() on the wrong object before realising it was actually coming from click.
@alexwlchan alexwlchan changed the title Passing an instance of Pathlib.Path to the test runner gets a TypeError Passing an instance of Pathlib.Path to CliRunner.invoke() gets a TypeError May 27, 2019
@joshuastorck
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@joshuastorck joshuastorck commented May 31, 2019

This code change would solve your problem in core.BaseCommand.main:

        if args is None:
            args = get_os_args()
        else:
            args = [arg.__fspath__() if hasattr(arg, "__fspath__") else arg
                    for arg in args]

However, that would still not make support for other types work, such as integers. In general, the parser assumes all inputs are strings. To properly handle this, a pre-processing step would have to be done to determine which arguments on the command line are associated with which types. However, this adds a lot of complexity, since command line arguments like dashes need to be handled. This would be a huge overhaul to the parser and is probably not a good idea.

I suggest closing this issue and just using the noted workaround.
@davidism davidism closed this May 31, 2019
@alexwlchan
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@alexwlchan alexwlchan commented May 31, 2019

I think it’s reasonable to say “we can’t coerce all arguments to strings”, but the confusing error message remains.

Would it be possible to add a check something like:

if not all(isinstance(arg, string_types) for arg in args):
    raise TypeError(“args must all be strings; got %r”)

to make it more obvious when somebody has made this mistake?
@davidism
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@davidism davidism commented May 31, 2019

If the documentation is unclear that the invoke-related APIs expect strings, that's something I'm ok with changing, but otherwise I think this is just expected behavior. In general, and I know this is somewhat contradictory given that Click does a bunch of validation, Python shouldn't be checking the types of arguments.
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Labels
good first issue save-for-sprint
4 participants
@jab @alexwlchan @joshuastorck @davidism