Datasets: [GSoC] Add Python 3 typing annotations to TFDS

[Conchylicultor]

Task: Add Python 3 typing annotations to TFDS repository. Now that Python 2 support is officially dropped, we can add better typing to TFDS.

Impact: Everyone using TFDS with a static type checker

Instructions:

• Add typing annotations to our API: (Typing annotation guide: https://docs.python.org/3/library/typing.html)
• Check that the typing annotations are valid with https://github.com/google/pytype
• Only update only a few files at a time (send multiple PR).
• As TFDS has many files, many people can work on this issue at the same time, just coordinate with each other.
• Updating the core/ is what matter the most. Then scripts/, Other files are optional
• Typing are ignored in test files, so no need to add typing annotations to *_test.py

Complexity: Easy

[abhinavsp0730]

Hi, I am Abhinav Prakash and I am working in this.

[vijayphoenix]

@Conchylicultor I was thinking of editing the my_dataset generator script, so that all new datasets will have Python3 typing annotations.
For example,

def _generate_examples(self) -> [Dictionary]:

Please share your views and guide me on the same
Thank you

[Conchylicultor]

@vijayphoenix, That's a good idea. To avoid boilerplate, you could add a core/types.py with:

KeyType = Union[str, bytes, int]
KeyExample = Tuple[KeyType, Dict[str, Any]]

And then have: _generate_examples() -> tfds.types.KeyExample:

[ashutosh1919]

@Conchylicultor, I have added first PR for this issue which adds pytype in 3 files. I will add multiple PRs and I will only include 3-4 files per PR so that it will be easy for reviewer to review.

Also, @abhinavsp0730 and @vijayphoenix , Please stay coordinated so that we don't overlap PRs. I am working on tfds/core outer files. If you are working then please work on tfds/core/(decode/download/features/proto/utils) files. Also, please review my PR and also give your comments since you two are working on same issue.

[Eshan-Agarwal]

Hey! I am working on core(/decode/download)

[Eshan-Agarwal]

@Conchylicultor and @ashutosh1919 can you check this PR #1571 and let me know if I am mistaking ?

[Ir1d]

Hi! I'm working on core/utils