Is this repo using mypy correctly?

[cclauss]

@dhruvmanila Is mypy running properly in our Travis CI runs? I believe that I made a mistake in #2464 which mypy is complaining about but it only seems to be raising issues in the maths subdirectory. Are we doing something wrong here?

[dhruvmanila]

Let me take a look at it and I'll get back to you.

[dhruvmanila]

I see the problem.
As mentioned in #2463 (comment), mypy ignores all the directories which don't contain the __init__.py file, and as the maths subdirectory contains the __init__.py file, mypy is only complaining about the errors in that specific directory. I will put the highlights here:

Updated metrics

There's already an open issue about it (Why do we need __init__.py files?): python/mypy#6385
Here's Guido van Rossum explaining what is going on: python/mypy#6385 (comment)

Out of 124 directories only 62 contains the __init__.py file and most of them are the project_euler/.. directories.

It's checking only for 116 files while there are around 736 files with extension py with around 124 directories according to:

$ fd -t f -e py --full-path Python/ | wc -l        # find files with extension py and count the lines
       736

$ fd -t d --full-path Python/ | wc -l                 # find directories and count the lines
       124

By running a simple bash script, I found that __init__.py exists only in these directories, but mypy will stop recursing into the subdirectories if it doesn't find __init__.py file in the parent directory. What I mean is it looks for Python files in ./Python/maths/ but not in ./Python/data_structures/stacks/ as there is no init file in data_structures directory.

__init__.py exists in ./Python/data_structures/hashing/number_theory/
__init__.py exists in ./Python/data_structures/linked_list/
__init__.py exists in ./Python/data_structures/stacks/
__init__.py exists in ./Python/digital_image_processing/
__init__.py exists in ./Python/digital_image_processing/dithering/
__init__.py exists in ./Python/digital_image_processing/edge_detection/
__init__.py exists in ./Python/digital_image_processing/filters/
__init__.py exists in ./Python/digital_image_processing/resize/
__init__.py exists in ./Python/digital_image_processing/rotation/
__init__.py exists in ./Python/maths/
__init__.py exists in ./Python/project_euler/problem_01/

...

And all the subdirectories of project_euler/..

For now, the only solution is to add the __init__.py files in all the directories and subdirectories (which can be easily done using a simple bash script).

[dhruvmanila]

I added the file in their respective directories and found this after running mypy --ignore-missing-imports Python/

Found 507 errors in 129 files (checked 736 source files) 😱

[cclauss]

OK. Can you please submit a PR that ONLY adds all these __init__.py files (that way we can revert the commit in the future if mypy comes up with a more rational approach). After we land that PR, we can create another PR that fixes the mypy issues and removes the || true. Thanks for your research on this topic.