Merging Dictionaries with Summed Values in Python

Day 15/365: Merging Two Dictionaries with Summed Values in Python 🧮🔗 Today I worked on a very common real-world task: merging two dictionaries where overlapping keys should have their values added together. 🧠 What this code does: I start with two dictionaries: d1 = {1: 10, 2: 20, 3: 30} d2 = {3: 40, 5: 50, 6: 60} Each key can represent something like: a product ID with its total sales, a student ID with total marks, a user ID with total points. The goal is to combine d2 into d1: If a key from d2 already exists in d1, I add the values. If the key doesn’t exist in d1, I insert it. Step by step: I loop over each key i in d2: for i in d2: For each key: If i is already a key in d1: I update d1[i] by adding d2[i] to it. Otherwise: I create a new entry in d1 with that key and its value from d2. After the loop finishes, d1 contains the merged result. For the given dictionaries: Key 3 exists in both, so its values are added: 30 + 40 = 70. Keys 5 and 6 only exist in d2, so they are added as new keys. Final output: {1: 10, 2: 20, 3: 70, 5: 50, 6: 60} 💡 What I learned: How to merge two dictionaries manually using a loop and conditions. How to update values in a dictionary when keys overlap. How this pattern appears in real data tasks like: combining monthly reports, merging user activity stats, aggregating counts from multiple sources. Next, I’d like to explore: Handling much larger dictionaries efficiently. Using dictionary methods like update() or Counter from collections to compare approaches. Trying the same logic with string keys (like product names) instead of numbers. Day 15 done ✅ 350 more to go. Got any other dictionary + loop problems (like counting frequencies from multiple sources or merging configs)? Drop them in the comments—I’d love to try them next. #100DaysOfCode #365DaysOfCode #Python #Dictionaries #DataStructures #LogicBuilding #CodingJourney #LearnInPublic #AspiringDeveloper

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