add missing __slots__ to containers and their base classes (#1144)

[ariebovenberg]

I have made things!

• slots added to many many classes
• in pytest plugin, the mechanism for tracking 'errors handled' needed a rework
• test added to prevent forgetting slots in the future

Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

Related issues

• Closes __slots__ = () missing in many base classes? #1144

Open questions

In adding __slots__, internal changes were needed to the pytest plugin. It works now (as discussed in #1144), but I still have a nagging feeling (monkey-patching and mutable global state will do that... 😉 )

I would like to suggest a follow-up change to the pytest plugin: that it undoes its patches after each test (like unittest.mock.patch does). The advantages are:

• classes are only patched when using the special ReturnsAsserts. This means it 100% doesn't affect any other tests (i.e. we get more predictable behavior). Currently all tests running after a returns-enabled test are patched, those before are not. A very nasty thing to debug if it ever messes with anybody's tests 👀
• the 'errors handled' mapping doesn't need to be a mutable global variable (👿) , it can be stored in the ReturnsAsserts instance.
• the 'errors handled' mapping doesn't need to be cleared after each test 🚀

🤔 Of course, we'll have to see what the performance impact is. Perhaps we might need to split the performance-heavy patching into a separate fixture, so it's only activated when needed

[sobolevn]

LGTM! Thanks!

[sobolevn]

classes are only patched when using the special ReturnsAsserts. This means it 100% doesn't affect any other tests (i.e. we get more predictable behavior). Currently all tests running after a returns-enabled test are patched, those before are not. A very nasty thing to debug if it ever messes with anybody's tests

Agreed!

the 'errors handled' mapping doesn't need to be a mutable global variable (👿) , it can be stored in the ReturnsAsserts instance.

Yes, I thought so too during code review.

[ariebovenberg]

I'll create a follow-up issue for the pytest plugin changes

There seems to be an issue with flake8 failing the the build, but not locally. Investigating...

[ariebovenberg]

It seems that for different python versions, flake8 attributes WPS602 errors to different lines of code. Double noqas were needed in pytest plugin. @sobolevn you can probably tell if this is a problem with the style guide, or flake8?

# passes in py37, but not py38+
class A:
    @staticmethod  # noqa: WPS602
    def foo():
        ...

# passes in py38+, but not py37
class A:
    @staticmethod
    def foo():    # noqa: WPS602
        ...

# passes on all versions:
class A:
    @staticmethod  # noqa: WPS602
    def foo():  # noqa: WPS602
        ...

[codecov]

Codecov Report

Merging #1147 (13cbf95) into master (51f91c7) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1147   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           79        79           
  Lines         2338      2415   +77     
  Branches       153       153           
=========================================
+ Hits          2338      2415   +77     

Impacted Files	Coverage Δ
returns/context/requires_context.py	100.00% <100.00%> (ø)
returns/context/requires_context_future_result.py	100.00% <100.00%> (ø)
returns/context/requires_context_ioresult.py	100.00% <100.00%> (ø)
returns/context/requires_context_result.py	100.00% <100.00%> (ø)
returns/future.py	100.00% <100.00%> (ø)
returns/interfaces/altable.py	100.00% <100.00%> (ø)
returns/interfaces/applicative.py	100.00% <100.00%> (ø)
returns/interfaces/bimappable.py	100.00% <100.00%> (ø)
returns/interfaces/bindable.py	100.00% <100.00%> (ø)
returns/interfaces/container.py	100.00% <100.00%> (ø)
... and 23 more

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[sobolevn]

@ariebovenberg yes, this is true 😞

[sobolevn]

I agree with your WPS issue, that things like __bases__, __module__, etc should be allowed.

Thanks a lot for working on this! 🎉