Add type hints

[sea-bass]

I want to do this so badly! But if someone wants to help, I won't be mad.

MyPy is promising: https://mypy-lang.org/, which has pre-commit hooks at https://github.com/pre-commit/mirrors-mypy

Would like to see how this plays with the docs generation as well.

[sea-bass]

I think the first order of business is to add mypy to the pre-commit check so it runs on CI:
https://github.com/pre-commit/mirrors-mypy

Unless this has a way to filter by folder, we may have to do the entire repo at once in order for CI to pass.

But if there is a way to filter this check by folder, it would be nice to break up the PRs. This is their official recommendation too:

https://mypy.readthedocs.io/en/stable/existing_code.html#start-small

I would recommend starting with a draft PR that applies this for one file, because I am interested in also seeing what it ends up looking like and how we have to modify the docstrings / docs generation so the docs look good with type annotations.

[kumar-sanjeeev]

There is a way to filter folders/ files/directories to exclude them from the mypy check. This can be done by enabling or using the --exclude option from the configuration file.

https://mypy.readthedocs.io/en/stable/config_file.html

I created a similar config file in the root dir and excluded the major directories in the repository from the mypy check. Now, I am able to run this file from the command-line interface like this:

mypy --config-file "CONFIG_FILE_NAME" .

This is running fine.

Now, because we want to configure mypy with pre-commit, I tried to read the config file from the pre-commit hook in the form of an argument. As of now, it is not working. I am figuring this out.

-   repo: https://github.com/pre-commit/mirrors-mypy
    rev: ''v1.10.1 " 
    hooks:
    -   id: mypy
        args: [--config-file, CONFIG_FILE_NAME]