ImportError: cannot import name 'BaseCommitizen' and others in files starting with `cz_`

[andres-fr]

Description

As it can be seen in the following line, all files present in the Python environment whose filename begins with cz_ will be discovered and iteratively loaded by commitizen. Unfortunately this also includes files that aren't in the scope of commitizen but happen to be in PYTHONPATH:

commitizen/commitizen/cz/__init__.py

Line 18 in 14b6c38

if name.startswith("cz_")

The reaction is very cryptic and can lead to long and frustrating debugging sessions. Fortunately it is known that the "cannot import" message is linked to circular dependencies, e.g. see https://stackoverflow.com/a/746655

Just importing commitizen doesn't break, but further recursive imports down the package trigger the issue.

Steps to reproduce

1. Create a file starting with cz_... and call e.g. from commitizen.commands.bump import Bump
2. Run that file with the python interpreter, making sure that the file's directory is in sys.path
3. The import will trigger an ImportError that is internal to commitizen like the one in the title.

Current behavior

Code that runs from interactive CLI doesn't run from script

Desired behavior

Code that runs on CLI should also run on script.

Environment

python --version Python 3.6.12 :: Anaconda, Inc.
python3 -c "import platform; print(platform.system())"

• commitizen version: 2.4.2
• python version: 3.6
• operating system: Ubuntu

[andres-fr]

I guess the main idea here is that a library shouldn't discover and load files from the python path by regex. That can be very tricky to find and could be even more problematic at other levels e.g. security. At the moment I'm kind of saturated and don't have any meaningful quickfix, apart from the obvious Don't ever name any Python file starting by cz_

[woile]

Sorry if it's a big frustrating 😞 , the plugin system can be improved, but it's based on a simple version of flask extension system.

There should be a way to avoid this kind of errors, I'm open to enhancements

[andres-fr]

Thanks for your answer, I would have to analyze more the plugin system to propose something more specific.
What do you think about this plugin architecture?

https://amir.rachum.com/blog/2017/07/28/python-entry-points/

[Lee-W]

I browse through the article you shared but not yet try it, but it looks like a good approach to me. Also, I just found how poetry can support similiar functionality. https://python-poetry.org/docs/pyproject/#plugins

[woile]

Interesting, I like it, seems quite intuitive. We'd have to update the template as well. Keep in mind, this would introduce a breaking change, but it's fine by me.

[andres-fr]

If you guys are comfortable with that I could give a hand in the next few weeks (we could do a hackathon or something) and try to refactor the CLI/plugin section. Only changes that you approve of course. I'd love to play around with poetry, seems neat

[Lee-W]

It sounds good to me. I just add a 3.0.0 tag to this issue.

[woile]

I'm in, great idea! Let's coordinate a date

[woile]

21 November 2020 I'll be joining to pycon argentina with a sprint for commitizen, hope you can join!