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Better __eq__ for generics #301

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ilevkivskyi opened this issue Oct 18, 2016 · 0 comments · Fixed by #308
Closed

Better __eq__ for generics #301

ilevkivskyi opened this issue Oct 18, 2016 · 0 comments · Fixed by #308

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@ilevkivskyi
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Currently, Iterable[T][int] == Iterable[int] returns False. It could be convenient to implement an __eq__ that returns True for generics that are considered the same from the point of view of static type checkers.

Of course, there is a very simple way to do this: just compare the new repr for two classes :-)
But probably the right way would be to factor out the algorithm from the new repr that "substitutes" type variables and use it for both repr and __eq__.
This was referenced Oct 21, 2016
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gvanrossum pushed a commit that referenced this issue Oct 29, 2016
@ilevkivskyi @gvanrossum
Refactor Union, Tuple, and Callable (#308)
50d2b4d 
Fixes #301 now ``List[Tuple[T, T]][int] == List[Tuple[int, int]]``
Fixes #298 now ``Table = Tuple[T, List[T]]`` can be used as generic type alias (as in PEP 484 example)
Fixes #299 now ``class MyTup(Tuple[int, ...]): ...`` is allowed
Fixes #156 (well, it does not substitute the annotations, but makes this task simple even in complex cases, see example in tests)

Also this PR fixes some minor things that I have found while working on this:
* ``List[Union]`` (with bare ``Union``, i.e. without arguments), ``List[Optional]``, ``List[Generic[T]]``, and ``List[ClassVar[int]]`` are not valid and are prohibited now.
* ``Generic`` did not evaluate forward references when asked, now it does.
* ``__qualname__`` was not copied on generic class subscription.
* Type was not erased on instantiation of subclasses of concrete containers (``List``, ``Set``, etc).
* There was an obscure bug in Python 2: sometimes ``_abc_registry`` was erased on instantiation.

The main idea of this PR is to fix the issues mentioned at the top by reusing the existing code. Namely, I pulled flattening and removing duplicates code from ``_Union`` and the tree calculation function ``_subs_tree`` from ``GenericMeta``. As well I moved ``Tuple`` and ``Callable`` _after_ ``GenericMeta`` and made them inherit the latter. So that now all types that could be generic store their info in common way using ``__origin__``, ``__parameters__``, ``__args__``.

I tried to polish this, to be sure that nothing was broken in the process of "refactoring" (also to improve speed). There is no recursion, the substitution tree is recalculated only when necessary. Also I added a lot of tests and many comments/docstrings (also for things added in my recent PRs).
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Refactor Union, Tuple, and Callable ilevkivskyi/typehinting
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