Ivan Levkivskyi added the comment:
I have submitted a PR with one of the quick fixes upstream (to python/typing).
Also I have played a bit with a more permanent fix. Here is an important
observation: it is not easy to avoid adding parameterized generics to
__subclasses__. For example, Node[int] should have at least one base, that base
will have it in __subclasses__. The former is dynamically updated, so that we
cannot "fool" it.
Also making subclass checks for all subclasses is a "deliberate act", so that
it should be treated by common rules.
It looks like we have only three options:
1. Abandon the idea of raising TypeError for generics, most users expect True
or False, so that some exiting code might break
2. Make __getitem__ for generics return self, so that ``Node[int] is Node`` at
runtime (this is a subset of the first option).
3. Still force people not to use issubclass() with parameterized generics (this
is quite bad idea and could have misleading consequences), but make an
exception for existing stdlib modules abc and functools, all later additions
should respect the rule.
4. Similarly to above, but just make tiny patches to abc and functools to use
__origin__ in subclass checks if it is present and not None.
Which option is the right one? I would vote for the last one. This could break
some (probably very small amount) existing code. So that formally speaking it
is a backward incompatible change. We could go with option 1 for 3.5 and with
option 4 for 3.6
Also I have found another failure in test suite with latest version from
python/typing after importing typing while running ./python -c 'import runpy,
typing; runpy.run_module("test")'
test test_collections failed -- Traceback (most recent call last):
File "/Users/ivan/hg-cpython/Lib/test/test_collections.py", line 1309, in
test_ByteString
self.assertNotIsInstance(memoryview(b""), ByteString)
AssertionError: <memory at 0x113b129b8> is an instance of <class
'collections.abc.ByteString'>
This is because of this line in typing.py
ByteString.register(type(memoryview(b'')))
The fix for this is very simple, we just need to decide whether memoryview
should be an instance of ByteString or not, and either remove this line or
remove the failing test.
I do not have any strong opinion on this, what do you think?
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