How to Pythonically Add Values When Merging Dictionaries?

How to Pythonically Merge Dictionaries with Value Addition

In Python, combining dictionaries can be a common task. One particular challenge is to merge two dictionaries while adding values for keys that appear in both.

For instance, consider the following dictionaries:

Dict A: {'a': 1, 'b': 2, 'c': 3}
Dict B: {'b': 3, 'c': 4, 'd': 5}

To obtain the desired result:

{'a': 1, 'b': 5, 'c': 7, 'd': 5}

We need to add the values of shared keys and retain the values of unique keys. To achieve this Pythonically, we can utilize the collections.Counter class.

from collections import Counter

A = Counter({'a':1, 'b':2, 'c':3})
B = Counter({'b':3, 'c':4, 'd':5})

result = A + B

Counters are essentially subclasses of dictionaries, so they provide similar functionality while adding value addition upon merging. The result dictionary now contains the combined values for shared keys and the original values for unique keys.

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