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AttributeError on __mypyc_env__ on Iterator that is yielded from twice and which calls a lambda #1210
Description
from typing import Iterator, Callable
def call_lambda(callable: Callable[[], None]) -> None:
pass
def get_iterator() -> Iterator[str]:
call_lambda(lambda: None)
yield ""
def yield_twice() -> Iterator[str]:
identified_imports = get_iterator()
yield from identified_imports
for identified_import in identified_imports:
yield identified_import
list(yield_twice())With mypyc test.py && python -c "import test" leads to:
❯ mypyc test.py && python -c "import test"
running build_ext
building 'test' extension
cc -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall -arch arm64 -mmacosx-version-min=11.0 -Wno-nullability-completeness -Wno-expansion-to-defined -Wno-undef-prefix -fPIC -I/private/tmp/mypy/mypyc/lib-rt -I/private/tmp/mypy/.venv/include -I/Users/daniel/.local/share/uv/python/cpython-3.14.0-macos-aarch64-none/include/python3.14 -c build/__native.c -o build/temp.macosx-11.0-arm64-cpython-314/build/__native.o -O3 -g1 -Werror -Wno-unused-function -Wno-unused-label -Wno-unreachable-code -Wno-unused-variable -Wno-unused-command-line-argument -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-ignored-optimization-argument -Wno-array-bounds -Wno-stringop-overread -Wno-stringop-overflow -Wno-cpp -Wno-array-bounds -Wno-stringop-overread -Wno-stringop-overflow
cc -bundle -undefined dynamic_lookup -arch arm64 -mmacosx-version-min=11.0 -LModules/_hacl -Wl,-headerpad,40 build/temp.macosx-11.0-arm64-cpython-314/build/__native.o -L/Users/daniel/.local/share/uv/python/cpython-3.14.0-macos-aarch64-none/lib -o build/lib.macosx-11.0-arm64-cpython-314/test.cpython-314-darwin.so
ld: warning: search path 'Modules/_hacl' not found
copying build/lib.macosx-11.0-arm64-cpython-314/test.cpython-314-darwin.so ->
Traceback (most recent call last):
File "<string>", line 1, in <module>
import test
File "test.py", line 19, in <module>
list(yield_twice())
File "test.py", line 16, in yield_twice
for identified_import in identified_imports:
File "test.py", line 7, in get_iterator
def get_iterator() -> Iterator[str]:
AttributeError: attribute '__mypyc_env__' of 'get_iterator_gen' undefinedThis is another issue I ran into while trying to compile isort with mypyc (PyCQA/isort#2586).
Code runs fine without mypyc compilation.
Activity
DanielNoord commentedon Aug 9, 2026
Fix in python/mypy#21826
Validated in PyCQA/isort#2586
[mypyc] Fix crash on double yielding Iterators (python#21826)
[mypyc] Fix crash on double yielding Iterators (#21826)
[mypyc] Fix crash on double yielding Iterators (#21826)