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Unexpected Infinite Loop While Using List Comprehension and Generator in Python 3.11

👀 Views: 3636 đŸ’Ŧ Answers: 1 📅 Created: 2025-09-01
python loops list-comprehension generators Python

I've been banging my head against this for hours. I'm encountering an unexpected infinite loop when trying to generate a list of even numbers from a range using a generator expression combined with a list comprehension in Python 3.11. The code I wrote looks like this: ```python def generate_evens(n): return [x for x in (x for x in range(n)) if x % 2 == 0] result = generate_evens(10) print(result) ``` I expected this code to return the list `[0, 2, 4, 6, 8]`, but instead, it seems to run indefinitely without producing any output. I've verified that the inner generator is functioning correctly by testing it separately: ```python for val in (x for x in range(10)): print(val) ``` This works fine and prints the numbers from 0 to 9. I also tried simplifying the comprehension like this: ```python def generate_evens_simple(n): return [x for x in range(n) if x % 2 == 0] ``` This returns the expected result without issues. I'm confused why combining a generator with a list comprehension causes it to hang. Is there a mistake in how the generator is being used, or is there an inherent issue with mixing these constructs? Any insights would be greatly appreciated! I'm working on a application that needs to handle this. I'd really appreciate any guidance on this.