Is there any pythonic way to combine two dicts (adding values for keys that appear in both)?

Question

For example I have two dicts:

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

I need a pythonic way of \'comb

Answer 1

The above solutions are great for the scenario where you have a small number of Counters. If you have a big list of them though, something like this is much nicer:

from collections import Counter

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

total = sum(list_of_counts, Counter())

print(total)
# Counter({'c': 7, 'a': 6, 'b': 5, 'd': 5, 'e': 3})

The above solution is essentially summing the Counters by:

total = Counter()
for count in list_of_counts:
    total += count
print(total)
# Counter({'c': 7, 'a': 6, 'b': 5, 'd': 5, 'e': 3})

This does the same thing but I think it always helps to see what it is effectively doing underneath.