Comprehension inlining: Bug if comprehension contains a lambda

@carljm

Code sample:

def outer(x):
    return [lambda: x for x in range(x)]

print([f() for f in outer(2)])

On 3.11, this produces [1, 1] as expected.

But on current main, I get:

>>> [f() for f in outer(2)]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in outer
TypeError: 'cell' object cannot be interpreted as an integer

Almost certainly due to PEP 709 / #101441, cc @carljm.

Linked PRs

gh-104357: fix inlined comprehensions that close over iteration var #104368

Thanks for finding this case! I had tests for similar cases with lambda inside the comprehension using the same name as non-cell outside the comprehension, but they were all of the form:

def outer():
    x = 2
    return [lambda: x for x in range(x)]

The key factor in your example is that there is no store to x in the outer scope, because it is an argument.

pythongh-104357: fix inlined comprehensions with cells

gh-104357: fix inlined comprehensions that close over iteration var (#…

Merge branch 'main' into supermon

Merge branch 'main' into fixloadsuperspec

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Comprehension inlining: Bug if comprehension contains a lambda #104357

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Comprehension inlining: Bug if comprehension contains a lambda #104357

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carljm commented on May 10, 2023

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