Python Type Annotations

[dgasmith]

Description

Bumps minimum python version to 3.6 according to NEP 29. We should bump to 3.7, but many libraries (torch!) are relatively slow to deprecate python versions, this seems like a reasonable compromise which allows us to type the library.

Questions

• [ ] Considering the range of inputs for contract/contract path, I'm leaning towards putting an Any on them for now. Any objections?
• [ ] ArrayType is a Union which could become a np.ndarray meaning all interfaces should use np.asanarray upon call to convert to np.ndarray types. It doesn't seem asanyarray is typed yet in the docs. Considering leaving these as Any as well since we tend to pass the base type through (called Tensor classes). Any guidance here?

Todos

Notable points that this PR has either accomplished or will accomplish.

• [x] Bump Python to >= 3.6
• [x] Add Python typing to the library
• [x] Add a MyPy merge gate

Status

• [ ] Ready to go

[codecov[bot]]

Codecov Report

Merging #161 (df6149e) into master (227c76b) will increase coverage by 0.41%. The diff coverage is 100.00%.

[dgasmith]

Thanks for the review @jcmgray. I think this is moving in the right direction, but we will need to revisit the typing interface for some of the more complex areas (dynamic programming, the diverse input types into contract, etc) before we put out a release.