dict.py

test1 = { 'cat' : 1, 'dog' : 1, 'bird' : 1}
test2 = { 'cat' : 3, 'dog' : 2, 'cow' : 2 }
for key, value in test1.items():
    test1[key] = test2.get(key, 0) + test1[key]

print(test1)