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gh-158407: Restore the C fast path for anext() - #158964
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leandrodamascena wants to merge 2 commits into
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leandrodamascena wants to merge 2 commits into
leandrodamascena wants to merge 2 commits into
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pythongh-157361 moved anext() to Python, which added a Python frame, a type() call and an attribute lookup to every call, and made the call itself go through the __anext__ slot wrapper for C types such as async generators. Implement anext() in C again, calling the am_anext slot directly. The two-argument form keeps using the Python coroutine from _pybuiltins, so that introspection tools can still see through it into the awaitable.
leandrodamascena
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ericsnowcurrently
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October 7, 2026 12:06
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Sorry but this still needs Kumar's output first. And I'm not really keen on having it back in Python (having it in Python helped the JIT) |
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This restores the C implementation of
anext()for the common one-argument case, calling theam_anextslot directly as before gh-157361. The two-argument form keeps using the Python coroutine from_pybuiltins, so the call graph improvement from gh-157361 still applies there.This follows the approach I proposed in #158407. I'm happy to change direction if there's a better way, especially with
aiter()in #157687 in mind.Local results (release build, ns per item):
anext(async_gen)anext(class_iter)anext(async_gen, default)anext(class_iter, default)async for(control)The one case that gets a bit slower is
anext()with a default on a Python class iterator, since the coroutine is now called from C instead of from Python.Two tests change as a result:
inspect.signature(anext)is back to unsupported (as in 3.15), and the traceback test only checks the coroutine frame, since theTypeErrornow comes from C.