exclude should imply a per-module follow import skip for matching modules #10377

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1. jwodder

   added

   bugmypy got something wrongmypy got something wrong

   on Apr 27, 2021
2. hauntsaninja commented on Apr 27, 2021

   

   hauntsaninja

   on Apr 27, 2021

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   This is a pretty reasonable confusion / ask.

   Here's some background:

   • Previously, mypy used __init__.py to figure out what directories are Python packages. However, this approach doesn't work with namespace packages (packages no longer need to have __init__.py in Python 3).
   • When we changed mypy's directory discovery logic to allow for namespace packages, it start finding things in various subtrees that mypy would previously ignore due to an absence of __init__.pys. --exclude was introduced as a way to ignore (newly) discovered files from being discovered.
   • However, --exclude currently only affects mypy's recursive file discovery logic (given a folder src, what files inside it should I check), and not its import following logic (src can import zillions of Python files from zillions of places, and mypy follows them all).
   • You can see the difference in practice by removing all imports of _version from your program and noticing that mypy won't check it, despite it being in src.

   That's all to say adding something like the following (in addition to --exclude) should work:

   [mypy-tinuous._version]
   follow_imports = skip
   

   I don't really expect users to understand all of that / seems reasonable to me that --exclude should do the equivalent of follow_imports=skip automatically. Might be a tiny bit tricky since one operates with module names and one operates with filenames and some subtleties to do with relative paths.
3. jwodder commented on Apr 27, 2021

   

   jwodder

   on Apr 27, 2021

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   @hauntsaninja That explains why just exclude = _version.py doesn't work, but it doesn't explain why exclude = src/tinuous/_(version|_init__).py and mypy src/tinuous/__main__.py don't work, as __main__.py doesn't import __init__.py or _version.py.
4. r-owen commented on Jul 6, 2021

   

   r-owen

   on Jul 6, 2021

   Last edited by r-owen

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   I found this ticket after being driven crazy by the same issue. But I can't make your suggested solution work with mypy 0.812. I am trying to check ts_salobj which has an auto-generated version.py (not present in the git repo) that is built before mypy runs and is not compatible with mypy. I have tried every variant of your suggested fix and none of them work, including even disabling follow_imports globally (which is not how I want to run):

   [mypy]
   ignore_missing_imports = True
   exclude = version.py  # or version\.py
   follow_imports = skip
   

   For the record, the line in version.py that makes mypy unhappy is:

   __dependency_versions__ = {}
   

   Any other suggestions for working around this issue? We can eventually fix the generated version.py, but not immediately and I would much rather not type-check that file.
5. r-owen commented on Jul 6, 2021

   

   r-owen

   on Jul 6, 2021

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   The solution I ended up with was two-fold:

   1. Avoid importing version.py when type checking:

   import typing
   
   if typing.TYPE_CHECKING:
       __version__ = "?"
   else:
       try:
           from .version import *
       except ImportError:
           __version__ = "?"
   

   2. Block version.py in two places in my setup.cfg file:

   [tool:pytest]
   addopts = --flake8 --mypy --ignore-glob=*version.py
   ...
   [mypy]
   ignore_missing_imports = True
   exclude = version\.py
   

   The [tool:pytest] section is sufficient to make pytest happy, but the exclude in the [mypy] section is useful when running mypy directly from the command line.
6. JelleZijlstra

   added

   topic-configurationConfiguration files and flagsConfiguration files and flags

   on Mar 19, 2022
7. hauntsaninja

   changed the title [-]Unable to instruct mypy to only check/exclude one file in package[/-] [+]exclude should imply a per-module follow import skip for matching modules[/+] on Oct 17, 2024