Make Mypy & JSON models friends

[sedwards2009]

This is some investigation work for making jsonmodel play nice with Mypy.

At the moment:

• Mypy can now understand that models have fields and to check assignments for valid field names.
• Mypy can now understand the data type of (some basic) model fields.

This is incomplete of course, but the progress is good.

It may be possible to make ListField accept a generics type and to eliminate this new duplication of code with the ListField constructor.

It seems unlikely that there is a way of explaining to Mypy that model constructors accept keyword arguments which correspond to the names of the model's fields. In this case manually adding a __init__() method with the correct types would work too.

The run_mypy.sh script can be used to put some of the code through mypy.

[sedwards2009]

This package looks useful for supporting Mypy generics and reducing redundant args to constructors. https://github.com/ilevkivskyi/typing_inspect i.e. you specify the generic types and the rest is automatic.

[sedwards2009]

http://mypy-lang.blogspot.com/2019/03/extending-mypy-with-plugins.html -> "Bundled plugins for standard library", describes how a plugin to mypy is used to add virtual typed methods to a class. This is basically the same problem we have in jsonmodels with respect to the model constructors.

[DanielSchiavini]

Related work: jazzband#165

[DanielSchiavini]

cool beans 👀