Question: 
Write a function to combine two dictionaries by adding values for common keys.


Model's Code:
def add_dict(dict1, dict2):
    result = {}
    keys = set(dict1) | set(dict2)
    for key in keys:
        result[key] = dict1.get(key, 0) + dict2.get(key, 0)
    return result



Sample Correct Code:
from collections import Counter
def add_dict(d1,d2):
   add_dict = Counter(d1) + Counter(d2)
   return add_dict


Asserts:
assert add_dict({'a': 100, 'b': 200, 'c':300},{'a': 300, 'b': 200, 'd':400})==({'b': 400, 'd': 400, 'a': 400, 'c': 300}) 
assert add_dict({'a': 500, 'b': 700, 'c':900},{'a': 500, 'b': 600, 'd':900})==({'b': 1300, 'd': 900, 'a': 1000, 'c': 900}) 
assert add_dict({'a':900,'b':900,'d':900},{'a':900,'b':900,'d':900})==({'b': 1800, 'd': 1800, 'a': 1800})


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 902 of 974: 695/902 (77.0509977827051%): success