Feature/type annotations

[midhun-pm]

PR adds

• Mypy Type annotations for the exposed traits api (in progress)

• A (minimal) testing framework for the type annotations

• Tests for the annotated types

[corranwebster]

I have a fairly strong recommendation to re-think the testing code. Rather than trying to extract code from within a function to run Mypy on, I'd go the much simpler route of having a tests.examples submodule containing the sample code you want to run Mypy on, and have the tests just grab a local .py file by path and feed it into Mypy directly.

[corranwebster]

This installs correctly for me and is working as expected now (within the limits of what has been implemented).

[codecov-io]

Codecov Report

Merging #904 into master will increase coverage by 0.79%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #904      +/-   ##
==========================================
+ Coverage    72.2%   72.99%   +0.79%     
==========================================
  Files          51       51              
  Lines        6367     6474     +107     
  Branches     1277     1302      +25     
==========================================
+ Hits         4597     4726     +129     
+ Misses       1379     1349      -30     
- Partials      391      399       +8

Impacted Files	Coverage Δ
traits/editor_factories.py	81.25% <0%> (-2.97%)	⬇️
traits/trait_list_object.py	75.09% <0%> (ø)	⬆️
traits/testing/unittest_tools.py	96.03% <0%> (ø)	⬆️
traits/trait_errors.py	83.33% <0%> (ø)	⬆️
traits/trait_handlers.py	61.02% <0%> (ø)	⬆️
traits/trait_numeric.py	51.65% <0%> (ø)	⬆️
traits/interface_checker.py	87.87% <0%> (ø)	⬆️
traits/api.py	90.32% <0%> (ø)	⬆️
traits/trait_notifiers.py	79.11% <0%> (ø)	⬆️
traits/constants.py	100% <0%> (ø)	⬆️
... and 10 more

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[corranwebster]

Playing around with this, we probably do need to have basic __init__ method signatures for the TraitTypes if the signature differs from the base TraitType signature. For example I am getting errors of the form "Enum has too many arguments" for constructs like Enum('foo', 'bar', 'baz').

We can use the @overload decorator if there are multiple different valid signatures (as is the case for Enum)

[mdickinson]

Before this is merged, please could you add a README text file at the top level of the traits-stubs directory that explains briefly what the code in this directory is doing and how to use it? We'll ultimately need more documentation than that, but a README would be enough for now.

[mdickinson]

A couple of other comments:

• the package is called traits-stubs, which is not a valid Python package name; maybe rename the package to traits_stubs (but keep the containing directory name of traits-stubs)? I'm not sure how / where this might matter, though.

• is the CI running the tests at the moment? If not, please could you open an issue for running the tests under the CI? (Or even better, fix in this PR, if the fix is easy.)

[corranwebster]

• the package is called traits-stubs, which is not a valid Python package name; maybe rename the package to traits_stubs (but keep the containing directory name of traits-stubs)? I'm not sure how / where this might matter, though.

The naming of the package is important, see PEP 0561

[corranwebster]

Yes, tests need to be run by CI and run successfully as part of this PR.

[mdickinson]

The naming of the package is important, see PEP 0561

Thanks. So to have a proper package structure for the tests, we may need to move the tests outside the traits-stubs directory. It may be worth checking how other stubs-providing packages do their testing.

[mdickinson]

N.B. For the Python 3.5 CI failures, it's probably enough to just replace open(some_path) with some_path.open(). While you're doing that, please also supply the encoding to the open call.

[mdickinson]

Thanks for the updates! Merging.