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

import itertools
import collections

dictA = {'a':1, 'b':2, 'c':3}
dictB = {'b':3, 'c':4, 'd':5}

new_dict = collections.defaultdict(int)
# use dict.items() instead of dict.iteritems() for Python3
for k, v in itertools.chain(dictA.iteritems(), dictB.iteritems()):
    new_dict[k] += v

print dict(new_dict)

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

OR

Alternative you can use Counter as @Martijn has mentioned above.