Pip: Cannot remove entries from nonexistent file

[niothiel]

• pip version: 20.0.2
• Python version: 3.7.6
• Operating system: OSX

Problem

It appears that when attempting to uninstall a package that was installed in editable mode, removing it does not work correctly if the lib/python3.7/site-packages/easy-install.pth file does not exist.

Reproduction

1. In a new folder, create a setup.py file:

from setuptools import setup

setup(
    name='repro',
    version='0.1dev',
)

1. Create a virtualenv: python3 -m venv env
2. Install in editable mode: env/bin/pip install -e .
3. Manually remove the file: rm env/lib/python3.7/site-packages/easy-install.pth
4. Attempt to uninstall the editable package: env/bin/pip uninstall repro
5. Observe error message: ERROR: Cannot remove entries from nonexistent file /..../env/lib/python3.7/site-packages/easy-install.pth

Expected Behavior

The uninstall should complete successfully, removing the .egg-link, even if the easy-install.pth file is not found.

Notes

In the wild, there is something that happens with our internal setup that causes the egg-link, to be created, but not the easy-install.pth file. I'm still trying to track down how this happens. Regardless of this, I believe that pip should not fail to uninstall when the file easy-install.pth doesn't exist, as the operation it would have done there would have just removed the entry from the file anyway.

I am happy to provide any further detail if needed. Thanks! :)

[uranusjr]

Sounds reasonable to me. The error message can continue to exist, but the uninstallation command does not need to fail. (It would help if pip has a mechanism to fail with a specific error code, but if the choice is between 1 and 0, I would prefer 0.)

[deveshks]

I can take this issue up and create the PR, but I have a question about the type of changes we want here.

If I understand correctly, we add easy-install.pth in files to remove here:
https://github.com/pypa/pip/blob/f6b5b40549583b65253b2de5a8ebfc3bf32cb3c1/src/pip/_internal/req/req_uninstall.py#L532

So in order to fix the issue, do we want to stop checking for easy-install.pth here? Or do we check for easy-install.pth but not raise an exception if it isn't found at

https://github.com/pypa/pip/blob/f6b5b40549583b65253b2de5a8ebfc3bf32cb3c1/src/pip/_internal/req/req_uninstall.py#L588-L592

[uranusjr]

We would still want to remove it if possible (and to emit an error message if it does not exist), so I’d say the latter. I did not read very deep into the implementation though, so there might be another way.

[deveshks]

Hi @uranusjr,

Okay, so do we want to emit the error message, but not cause the installation to fail by perhaps wrapping https://github.com/pypa/pip/blob/f6b5b40549583b65253b2de5a8ebfc3bf32cb3c1/src/pip/_internal/req/req_uninstall.py#L532
in a try catch?

Or instead of raising an error at https://github.com/pypa/pip/blob/f6b5b40549583b65253b2de5a8ebfc3bf32cb3c1/src/pip/_internal/req/req_uninstall.py#L588-L592
we can raise a warning using the warnings module, or just log the error and continue

[deveshks]

Hi @uranusjr ,

If my above suggestions make sense now, I can go ahead and create a PR for the same

[uranusjr]

I like the second approach more; it’s probably enought to logger.warning the message and move on.

[deveshks]

Thanks @uranusjr for the response. I will create a PR to do the same.