👀 Views: 47 💬 Answers: 1 📅 Created: 2025-06-01

python list-comprehensions error-handling Python

I'm working on a project and hit a roadblock. I'm relatively new to this, so bear with me. I'm working on a project and hit a roadblock. I'm working on a project and hit a roadblock. I'm working with a frustrating scenario with a list comprehension in my Python 3.10 application. It seems I'm trying to access elements in a list that might not be initialized properly, but I'm not quite sure how to diagnose the question. The behavior I'm seeing is `TypeError: 'NoneType' object is not subscriptable`. Here’s the relevant snippet of my code: ```python class DataProcessor: def __init__(self, data): self.data = data def process_data(self): # I expect 'data' to be a list of dictionaries return [item['value'] for item in self.data if item is not None] # Example of how I'm using this class processor = DataProcessor(None) # This is where I think the question starts results = processor.process_data() ``` In the example above, I pass `None` to the `DataProcessor`, and then when I try to process the data, the comprehension fails. I thought that the `if item is not None` check would prevent the scenario, but it appears that the scenario lies with `self.data` being `None` in the first place. I've tried adding a check in the constructor to ensure that `data` is always a list, like this: ```python class DataProcessor: def __init__(self, data): self.data = data if data is not None else [] ``` However, when I run the code now, I don't see the expected behavior. The results variable ends up being an empty list, which is fine, but I want to know if there is a better approach. Should I raise an exception instead of silently returning an empty list? What are the best practices for handling such cases in Python? Any guidance would be appreciated! I'm working on a API that needs to handle this. The stack includes Python and several other technologies. Any advice would be much appreciated. Has anyone dealt with something similar? I'm using Python stable in this project. I appreciate any insights!