platform-specific dependencies failure

[fersarr]

When using platform-specific dependencies as documented in setuptools docs, I am running into an issue:

In Python 3.7

>>> import pkg_resources as pr
>>> pr.get_distribution('doesntexist;python_version<"3.0"')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 479, in get_distribution
    dist = get_provider(dist)
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 355, in get_provider
    return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
IndexError: list index out of range

However, when the dependency is for the version of python we are running on, the outcome is as expected

>>> pr.get_distribution('doesntexist;python_version>"3.0"')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 479, in get_distribution
    dist = get_provider(dist)
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 355, in get_provider
    return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 898, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/users/is/fsaraviarajal/workspace/conda_envs_test/test3_offlinecopyof2/lib/python3.7/site-packages/pkg_resources/__init__.py", line 784, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'doesntexist; python_version > "3.0"' distribution was not found and is required by the application

I have reproduced this on versions of 28.8.0 and 40.7.3 of setuptools

The exception IndexError: list index out of range comes from this line:

setuptools/pkg_resources/__init__.py

Line 357 in c1243e9

return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]

[pganssle]

@fersarr What is the result you expect? Another DistributionNotFound error? A different error type entirely? No error and returning None or something?

From what I can tell in the documentation, the idea of environment markers is not mentioned at all. For packages that do exist, it seems like they return the distribution regardless of whether or not the environment marker is met.

Not sure what the right behavior is. I'm leaning in favor of raising some sort of error since that's already what happens anyway. If people want to take the environment markers into account, we could theoretically make the error raised a subclass of DistributionNotFound like DistributionEnvironmentMismatch or something.

[fersarr]

Hi @pganssle. In the docs link you provided, these are in fact mentioned. Look under Requirements Parsing or just search for "python_version" in your link. For example, it says:

The “markers” in a requirement are used to specify when a requirement should be installed – the requirement will be installed if the marker evaluates as true in the current environment. For example, specifying argparse;python_version<"3.0" will not install in an Python 3 environment, but will in a Python 2 environment

I think the behaviour in this case should not be DistributionNotFound because it was not meant to be found anyway. And it should not stay as IndexError. But like you said, I am not entirely sure what it should be. Perhaps a None should be returned like you said or a special kind of exception indicating that the distribution you asked for is not for this environment.

[pganssle]

Yes I understand what markers are in the context of install requirements, but not how they should modify get_distribution . They work fine in install_requires and other similar contexts where they clearly have a meaning, but get_distribution retrieves things that are already installed.

Can you clarify your use case?