gh-132493: Support deferred annotations in Protocols #132494
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sobolevn
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Apr 14, 2025
| class DeferredProto(Protocol): | ||
| x: DoesNotExist | ||
| self.assertEqual(get_protocol_members(DeferredProto), {"x"}) | ||
| self.assertEqual( |
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Question: when should we test all formats and when just one is enough?
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I guess in this case Protocol is not doing anything very sophisticated with its annotations, so we can just run a basic test to make sure it works.
sobolevn
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Apr 15, 2025
AlexWaygood
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Apr 15, 2025
|
I wonder if we could lazily create the protocol members list? But we can explore that separately. |
JelleZijlstra
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Apr 16, 2025
pythongh-132494 made typing.py eagerly import annotationlib again because typing contains several protocols. Avoid this by determining annotations lazily. This should also make protocol creation faster: Unpatched: $ ./python.exe -m timeit -s 'from typing import Protocol, runtime_checkable' '''@runtime_checkable class MyProtocol(Protocol): def meth(self): pass ''' 50000 loops, best of 5: 9.28 usec per loop $ ./python.exe -m timeit -s 'from typing import Protocol, runtime_checkable' '''class MyProtocol(Protocol): def meth(self): pass ''' 50000 loops, best of 5: 9.05 usec per loop Patched: $ ./python.exe -m timeit -s 'from typing import Protocol, runtime_checkable' '''@runtime_checkable class MyProtocol(Protocol): def meth(self): pass ''' 50000 loops, best of 5: 7.69 usec per loop $ ./python.exe -m timeit -s 'from typing import Protocol, runtime_checkable' '''class MyProtocol(Protocol): def meth(self): pass ''' 50000 loops, best of 5: 7.78 usec per loop This was on a debug build though and I haven't compared it with versions where Protocol just accessed `.__annotations__` directly, and it's not a huge difference, so I don't think it's worth calling out the optimization too much. A downside of this change is that any errors that happen during the determination of attributes now happen only the first time isinstance() is called. This seems OK since these errors happen only in fairly exotic circumstances. Another downside is that any attributes added after class initialization now get picked up as protocol members. This came up in the typing test suite due to `@final`, but may cause issues elsewhere too.
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