ModuleNotFoundError: No module named 'flit_core.dummy'

[nschloe]

I'm building my project with

[build-system]
requires = ["flit_core >=3.2,<4"]
build-backend = "flit_core.buildapi"

and since earlier today I'm getting the error message

      [...]
      ModuleNotFoundError: No module named 'flit_core.dummy'
      [end of output]

when running pip install . on the repo. Perhaps I messed up something in the package, but the error message points towards flit. Any idea what's going on?

[uSpike]

This is hitting my projects as well which use pre-commit to install flakeheaven. A debug log is attached

pre-commit.log

[takluyver]

This is almost certainly related to #499. Based on the logs here and in #529, I'd guess this occurs when a) it can't get __version__ by static analysis, so it falls back to running code, and b) __init__.py contains a relative import.

It looks like this is going to hit a load of people - sorry about that. I'll ask people now: please don't comment just to say it affects you too (you can click the 👍 under the first comment).

I am pretty busy, so any help working out how to deal with this is welcome. Besides #499, you might want to look at commit 432dc76 where the 'dummy' module names were introduced, and the backwards-compatibility implementation of load_module in importlib which we were using before the changes in #499.

[nschloe]

I'd guess this occurs when a) it can't get version by static analysis,

Indeed! I set the version to static in pyproject.toml and pip install . shows some import errors that I can work with. I guess flit bumped into those when trying to resolve dynamic=["version"], and just didn't manage to forward the error message.

[takluyver]

I should have mentioned, there are two levels of static vs dynamic in getting the version number. You can set it in pyproject.toml, you can have a plain __version__ = '1.0' statement in __init__.py which Flit will read without executing the code, or you can have something more complex which requires Flit to execute the code. This issue only affects the last case (look for the function get_docstring_and_version_via_import in the traceback).

[nschloe]

Yup, I have the version number in __about__.py, and it's imported from there in __init__.py and other places. That's how I ran into the issue.

[taut-and-yare]

I am getting it from csselect2 due to relative imports in init here

[takluyver]

Again, I know this issue is going to affect a lot of people. There will hopefully be a fix soon. In the meantime, please 👍 the initial comment if you just want to say 'me too'. Thanks!

[takluyver]

Based on a tiny test case, I think #531 fixes this. It would be great if some people affected by it on real projects could try it out and see if there are other issues lurking. Install from that branch, and then try either flit build or pip install . --no-build-isolation.

[henryiii]

FYI, the docs seem to be out of date. The "3.7.1" milestone confused me for a second, because the "current" version in the docs is 3.5.1.

[liZe]

It would be great if some people affected by it on real projects could try it out and see if there are other issues lurking.

It seems to work well for me. Thanks a lot for the quick fix.

[takluyver]

It looks like the docs stopped building when we renamed master to main (readthedocs/readthedocs.org#7907). I've just updated the RTD config, hopefully it will be happy now.

[nschloe]

It would be great if some people affected by it on real projects could try it out

Still not working for me with dynamic = ["version"].

[takluyver]

@nschloe could I ask you to give a bit more detail of what your code is like, what you're doing and what you see (more of the traceback)? If you're using pip, pass --no-build-isolation just to test this, otherwise it will set up a temporary build environment and install flit_core 3.7.0 from PyPI.

[henryiii]

You can also just set the URL in the pyproject.toml's requires section, like:

requires = ["flit_core @ git+https://github.com/pypa/flit@i530"]

(Hmm, at least I think so - haven't tried that with a dual package yet like flit/flit_core - I think there's a way to set a subdirectory. Maybe add &subdirectory=flit_core?)

Edit: Yeah, I don't know how to put a subdirectory in here. :(

[nschloe]

I just run any flit command, e.g., flit publish, on nschloe/colorio to get the error. I can provide more details tomorrow.

[henryiii]

The correct syntax (thanks @layday) is:

requires = ["flit-core @ git+https://github.com/pypa/flit@i530#subdirectory=flit_core"]

I tried this out:

$ brew install git-lfs
$ gh repo clone nschloe/colorio
$ cd colorio

Removing the cap on flit version causes pip install . to fail. Changing to the line above fixes it!

🚢

[nschloe]

Thanks @henryiii for looking up the correct syntax! With this, it also works for me.

[createcandle]

Same issue here. I'd be happy to test the fix if there is a clear step by step explanation of how to try that.

[nschloe]

@createcandle #530 (comment)

[createcandle]

@nschloe Thanks, but for me that's missing a few steps ':-)

[takluyver]

OK, it seems like #531 fixes this. I'll merge that and make a new release (3.7.1).

[takluyver]

& thanks for testing it!