[issue39166] Python 3.9.0a2 changed how "async for" traces its final iteration

[Ned Batchelder]

Ned Batchelder <ned at nedbatchelder.com> added the comment:

I see that you are right, the bytecode is the same in 3.8 and 3.9. Nevertheless, the trace has definitely changed.  Using the same program from the top of the issue, here are the ends of the traces for a number of Python versions.  The extra trace of line 32 appears in 3.9.0a2:


$ for v in 3.6.9 3.7.4 3.8.1 3.9.0a1 3.9.0a2; do printf "\n--------\n"; $(pythonz locate $v) -c "import sys; print(sys.version)"; $(pythonz locate $v) /tmp/bpo2.py | tail -10; done

--------
3.6.9 (default, Jul 29 2019, 08:21:55)
[GCC 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.10.44.4)]
line 21:             return next(self._it)
exce 21:             return next(self._it)
line 22:         except StopIteration:
line 23:             raise StopAsyncIteration
exce 23:             raise StopAsyncIteration
retu 23:             raise StopAsyncIteration
exce 31:     async for letter in AsyncIteratorWrapper("ab"):
line 33:     print(".")
.
retu 33:     print(".")

--------
3.7.4 (default, Jul 11 2019, 19:53:42)
[Clang 10.0.0 (clang-1000.10.44.4)]
line 21:             return next(self._it)
exce 21:             return next(self._it)
line 22:         except StopIteration:
line 23:             raise StopAsyncIteration
exce 23:             raise StopAsyncIteration
retu 23:             raise StopAsyncIteration
exce 31:     async for letter in AsyncIteratorWrapper("ab"):
line 33:     print(".")
.
retu 33:     print(".")

--------
3.8.1 (default, Dec 19 2019, 08:38:38)
[Clang 10.0.0 (clang-1000.10.44.4)]
line 21:             return next(self._it)
exce 21:             return next(self._it)
line 22:         except StopIteration:
line 23:             raise StopAsyncIteration
exce 23:             raise StopAsyncIteration
retu 23:             raise StopAsyncIteration
exce 31:     async for letter in AsyncIteratorWrapper("ab"):
line 33:     print(".")
.
retu 33:     print(".")

--------
3.9.0a1 (default, Nov 20 2019, 18:52:14)
[Clang 10.0.0 (clang-1000.10.44.4)]
line 21:             return next(self._it)
exce 21:             return next(self._it)
line 22:         except StopIteration:
line 23:             raise StopAsyncIteration
exce 23:             raise StopAsyncIteration
retu 23:             raise StopAsyncIteration
exce 31:     async for letter in AsyncIteratorWrapper("ab"):
line 33:     print(".")
.
retu 33:     print(".")

--------
3.9.0a2 (default, Dec 19 2019, 08:42:29)
[Clang 10.0.0 (clang-1000.10.44.4)]
exce 21:             return next(self._it)
line 22:         except StopIteration:
line 23:             raise StopAsyncIteration
exce 23:             raise StopAsyncIteration
retu 23:             raise StopAsyncIteration
exce 31:     async for letter in AsyncIteratorWrapper("ab"):
line 32:         print(letter)
line 33:     print(".")
.
retu 33:     print(".")

$

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<https://bugs.python.org/issue39166>
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