Unexpected behavior with `itertools.groupby` on sorted list in Python 2.7
I've been banging my head against this for hours. Hey everyone, I'm running into an issue that's driving me crazy. I'm dealing with Does anyone know how to I've searched everywhere and can't find a clear answer..... I've been struggling with this for a few days now and could really use some help... I'm encountering an unexpected behavior when using `itertools.groupby` on a sorted list in Python 2.7. I have a list of dictionaries that I want to group by a specific key, but it seems that `groupby` is not functioning as I expected. Here’s my code: ```python from itertools import groupby data = [ {'id': 1, 'value': 'A'}, {'id': 2, 'value': 'A'}, {'id': 3, 'value': 'B'}, {'id': 4, 'value': 'B'}, {'id': 5, 'value': 'C'} ] # Sorting the data by the 'value' key sorted_data = sorted(data, key=lambda x: x['value']) # Using groupby to group by 'value' grouped_data = groupby(sorted_data, key=lambda x: x['value']) for key, group in grouped_data: print(key, list(group)) ``` The expectation is that the output should group the dictionaries by the `value` key, like this: ``` A [{'id': 1, 'value': 'A'}, {'id': 2, 'value': 'A'}] B [{'id': 3, 'value': 'B'}, {'id': 4, 'value': 'B'}] C [{'id': 5, 'value': 'C'}] ``` However, I sometimes end up with empty groups or incorrect associations, especially when I try to modify the `data` list by adding more entries with the same `value`. This is peculiar since I am sorting the data before calling `groupby`, which I thought was necessary. I've tried checking the sorting step and even printed the `sorted_data` to ensure it looks correct, which it does. I also verified that the `value` keys are all consistent and correctly formatted. Could there be an issue with how `groupby` works when dealing with mutable data structures or changes in the list after grouping? What might I be missing here? What am I doing wrong? This is my first time working with Python LTS. I appreciate any insights! This issue appeared after updating to Python stable. What's the best practice here? This is my first time working with Python latest. Any examples would be super helpful.