chore[python]: Turn on mypy strict mode

[zundertj]

See the comment in pyproject.toml. It basically means we have not changed that much, as we still ignore the warning. But there is not really a feasible way until PyO3 supports generating type annotations. Otherwise, maintaining stubs would just be a huge waste of resources, as it is duplicating the "outer" python api.

Ticks the last box on the mypy list in #4044

[stinodego]

No need to add this to overrides, we can just do:

[tool.mypy]
strict = true
warn_return_any = false

I agree that manually adding stub files is overkill.

[zundertj]

That would override it for all modules, i.e. also numpy, pandas, etc. I would prefer to make the selection as small as possible.

[stinodego]

That would override it for all modules, i.e. also numpy, pandas, etc. I would prefer to make the selection as small as possible.

You're right; I didn't think this through 😄

We still need the ignore imports override though. So you could add an additional section of overrides with just the Polars package and the warn_return_any in it.

EDIT: Actually, you can't ignore polars.polars in the overrides specifically. The mypy errors happen in the Python polars package. So that would mean that my suggestion was actually correct. What do you mean with this affecting numpy, pandas?

[codecov-commenter]

Codecov Report

Merging #4415 (b3dc257) into master (beb802a) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4415      +/-   ##
==========================================
+ Coverage   78.98%   79.01%   +0.02%     
==========================================
  Files         483      483              
  Lines       77094    77111      +17     
==========================================
+ Hits        60895    60926      +31     
+ Misses      16199    16185      -14     

Impacted Files	Coverage Δ
...polars-time/src/chunkedarray/rolling_window/mod.rs	71.53% <0.00%> (-0.77%)	⬇️
polars/polars-lazy/src/logical_plan/alp.rs	84.39% <0.00%> (-0.73%)	⬇️
py-polars/polars/testing.py	94.14% <0.00%> (-0.54%)	⬇️
...olars/polars-core/src/frame/groupby/into_groups.rs	58.12% <0.00%> (-0.28%)	⬇️
polars/polars-lazy/src/physical_plan/planner/lp.rs	88.11% <0.00%> (+0.02%)	⬆️
polars/polars-lazy/src/logical_plan/conversion.rs	78.34% <0.00%> (+0.12%)	⬆️
polars/polars-core/src/series/mod.rs	64.20% <0.00%> (+0.15%)	⬆️
polars/polars-core/src/fmt.rs	73.07% <0.00%> (+0.18%)	⬆️
polars/polars-core/src/datatypes/mod.rs	72.40% <0.00%> (+0.18%)	⬆️
...ars-arrow/src/kernels/rolling/no_nulls/variance.rs	88.55% <0.00%> (+0.23%)	⬆️
... and 6 more

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[zundertj]

Python 3.7 test is fixed in #4416.

[stinodego]

I think you forgot to push your latest changes removing fsspec and pyarrow from the overrides. The Python test fix has been merged, so with a rebase + push I think we're good to go!

[stinodego]

Awesome! 🚀

[ritchie46]

That's quite an achievement. Well done. 👍