👀 Views: 521 💬 Answers: 1 📅 Created: 2025-06-26

python list-comprehensions scope Python

I've spent hours debugging this and I'm having trouble with I’m working with an scenario with variable scope when using a loop variable within a list comprehension... In Python 3.9, I expected the loop variable `i` to be scoped only within the comprehension, but I encountered unexpected behavior when trying to reference `i` after the comprehension. Here’s a simplified version of what I’m trying to do: ```python result = [i * 2 for i in range(5)] print(i) # What should this output? ``` I thought `i` would be out of scope after the list comprehension, but when I run this code, it outputs `4`. I was expecting a `NameError` since `i` should only exist within the comprehension. I found this behavior surprising, especially since I’m coming from a JavaScript background where `let` confines the variable scope. I tried using a generator expression instead, like this: ```python result = (i * 2 for i in range(5)) print(i) # Still outputs 4 ``` In both cases, `i` retains its value after the comprehension or generator expression finishes. I even attempted to wrap the comprehension in a function to limit the scope: ```python def generate_result(): return [i * 2 for i in range(5)] generate_result() print(i) # This still outputs 4 ``` Why does `i` remain accessible outside the comprehension or function, and is there a way to avoid this behavior? I want to ensure my code behaves as expected and prevents unintended side effects from variable scope. Any insight into this would be greatly appreciated! My development environment is macOS. Am I missing something obvious? This is part of a larger web app I'm building. Any pointers in the right direction? Cheers for any assistance!