👀 Views: 32 💬 Answers: 1 📅 Created: 2025-06-13

python dictionary merge lists Python

I'm refactoring my project and I'm working on a personal project and I'm trying to merge two dictionaries in Python where the values are lists of strings, but I'm working with an scenario where the resulting values are not being combined as expected. For example, given two dictionaries: ```python dict_a = {'key1': ['a', 'b'], 'key2': ['c']} dict_b = {'key1': ['d'], 'key2': ['e', 'f']} ``` I want to merge these two dictionaries such that for each key, the values are concatenated into a single list. The expected output should be: ```python merged_dict = {'key1': ['a', 'b', 'd'], 'key2': ['c', 'e', 'f']} ``` However, my current approach using a loop to merge them results in overwriting the list instead of appending: ```python merged_dict = {} for key in dict_a.keys(): merged_dict[key] = dict_a[key] for key in dict_b.keys(): merged_dict[key] = dict_b[key] ``` This gives me: ```python {'key1': ['d'], 'key2': ['e', 'f']} ``` What I really need is to append the values from `dict_b` to the lists in `dict_a` when the keys match. I also checked if the keys exist in both dictionaries before appending, but I’m not sure how to do this correctly. I tried using the `setdefault` method, but it didn't work as intended. Any insights or best practices on how to handle this merging of list values in dictionaries would be greatly appreciated. I'm using Python 3.9. How would you solve this? This issue appeared after updating to Python 3.9.