Python: Inconsistent loop behavior when processing lists with varying lengths in a multi-threaded environment
I'm attempting to set up I'm confused about I'm stuck on something that should probably be simple..... I'm working on a project and hit a roadblock... I'm currently working on a multi-threaded application in Python 3.9, and I'm experiencing some inconsistent behavior when looping through a list of varying lengths. I have a list of data that gets populated by multiple threads, and I'm trying to process this data in a for loop to perform some calculations. However, sometimes I run into an `IndexError`, and I need to figure out why it's happening. Here's a simplified version of my code: ```python import threading import time data_list = [] def populate_data(): for i in range(5): data_list.append(i) time.sleep(0.1) # Simulate delay in data population threads = [] for _ in range(3): thread = threading.Thread(target=populate_data) threads.append(thread) thread.start() # Give threads some time to populate data for thread in threads: thread.join() # Process the data for i in range(len(data_list)): if data_list[i] % 2 == 0: print(f'Processing even number: {data_list[i]}') else: print(f'Processing odd number: {data_list[i]}') ``` In my testing, `data_list` sometimes ends up being shorter than expected, which leads to an `IndexError` when the loop tries to access an index that doesn't exist. I suspect this is happening because I’m trying to read from `data_list` while it’s still being modified by other threads. I’ve tried using a lock around the population step, but that didn't resolve the scenario. Here's what I attempted with the lock: ```python lock = threading.Lock() def populate_data(): for i in range(5): with lock: data_list.append(i) time.sleep(0.1) ``` Even with this change, I still encounter the `IndexError`. Is there a better way to handle this scenario, or should I consider using a different data structure? Any insights or best practices for managing shared data in a multi-threaded environment would be greatly appreciated! This is part of a larger service I'm building. Thanks in advance! How would you solve this? Any ideas how to fix this? I'm working on a CLI tool that needs to handle this. I'd love to hear your thoughts on this.