Confusion with loop indexing when modifying a nested list in Python
I'm migrating some code and I've searched everywhere and can't find a clear answer... I'm working with an scenario with loop indexing while trying to manipulate a nested list in Python. I'm using Python 3.10, and my goal is to flatten a 2D list, but I'm running into unexpected behavior when I attempt to modify the nested lists during iteration. Here's a simplified version of my code: ```python nested_list = [[1, 2], [3, 4], [5, 6]] flattened_list = [] for sublist in nested_list: for item in sublist: flattened_list.append(item) if item % 2 == 0: sublist.remove(item) ``` After running this code, I expected `flattened_list` to contain all numbers and `nested_list` to have the even numbers removed. However, I got an `IndexError` at runtime, indicating that I was trying to access an index that no longer exists. It seems like modifying `sublist` while iterating over it led to this behavior. I even tried using `list.copy()` to work on a copy of `sublist`, but that didn't solve the question. How can I achieve my goal of flattening the list while safely removing even numbers from the original nested structure without running into indexing errors or skipping elements? Am I missing something obvious? This is part of a larger API I'm building. Has anyone else encountered this? I recently upgraded to Python 3.10. Cheers for any assistance!