[WIP] fix mypy errors

[utkarsh-maheshwari]

Description

Fixed mypy errors mentioned in #1528 (comment) by adding type hints to var_names and latex_elements. Addresses #1581

Checklist

• Follows official PR format
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

[codecov]

Codecov Report

Merging #1586 (c9db950) into main (a9e5812) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1586   +/-   ##
=======================================
  Coverage   90.05%   90.05%           
=======================================
  Files         108      108           
  Lines       11584    11584           
=======================================
  Hits        10432    10432           
  Misses       1152     1152           

Impacted Files	Coverage Δ
arviz/plots/traceplot.py	95.55% <100.00%> (ø)

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[utkarsh-maheshwari]

Checks are passed but how should I check if the mypy errors have been resolved?

[OriolAbril]

There should only be a mypy.ini file that covers the whole package. Both the mypy.ini file and pinning mypy 0.790 will be done by #1528 as a temporal fix. Temporal because they are not fixing the issue, they are only ignoring it and sliencing it for a while so we can keep ahead and start using typing_copilot as soon as possible.

To fix the errors you'll have to edit the actual arviz library, nothing should be modified in the examples folder. The first errors listed in the other PR for example are complaining that var_names is a tuple instead of a list. This is a false positive, the mistake is in the type hints that the function (plot_trace in this case) has. This is the line that defines the type hint in question:

arviz/arviz/plots/traceplot.py

Line 15 in a9e5812

var_names: Optional[List[str]] = None,

List is not the correct type hint, a tuple or a numpy array are perfectly valid options. Thus, the type hint should use Sequence instead of list.

To run mypy I believe you have to run mypy -p arviz from the base folder, but if I understand correctly, it will only work if you have the mypy.ini defined in #1528.

[utkarsh-maheshwari]

Okay. So I have changed the type hint for var_names. First six have been resolved now.

The major doubt that I am having is before changing the type hint to Sequence, I run the command by pinning 2 different versions of mypy
typing_copilot init --overwrite

I can see the 7 errors in case I pin mypy==0.812 but not if I pin mypy==0.790. So, according to #1528 (comment) option 1, if we pin mypy<0.800, do we really need to change the type hint?

[OriolAbril]

So, according to #1528 (comment) option 1, if we pin mypy<0.800, do we really need to change the type hint?

Yes, because the ideal solution is doing option 2. Option 1 is a temporal fix that allows us to continue working on #1528 and not have to wait until we have time to fix all the issues (as we are all volunteers, it is not clear when we would have time and if it takes us too long maybe by the time we get to do it instead of 7 there are 30 errors).

We are doing similar things with #1578 where we disabled some pylint checks to get CI to pass quickly but we did not fix those issues, or with #1537 where we have temporarily disabled pyjags tests because pyjags requires numpy >=1.20 and tensorflow probability requires numpy <=1.19 because our tfp converter is outdated. Fixing the converter is complicated and depends also on changes on tfp side so we feel it's better to wait for now until we can update the code and fix the root issue, if we updated the code now, we may have to rewrite it again in a few months

[utkarsh-maheshwari]

Okay I got it now. Very nicely explained. Thank you!

[utkarsh-maheshwari]

Do these changes needed to be listed in changelog?

[OriolAbril]

I don't think so, thanks! I am realizing that there are many other places where we have inputs type hinted as lists when they should be sequences. I will merge this to go ahead with typing copilot directly with latest mypy but keep the issue open.