I have two dictionaries and I need to combine them. I need to sum the values of similar keys and the different keys leave them without sum.

These are the two dictionaries:

d1 = {'a': 100, 'b': 200, 'c':300}

d2 = {'a': 300, 'b': 200, 'd':400}

The expected results:

d3= {'b': 400, 'd': 400, 'a': 400, 'c': 300}

I have successfully made the sum and added them to this third dictionary, but I couldn't know, how to add the different values.

My try

d1 = {'a': 100, 'b': 200, 'c':300}

d2 = {'a': 300, 'b': 200, 'd':400}

d3 = {}

for i, j in d1.items():

for x, y in d2.items():

if i == x:

d3[i]=(j+y)

print(d3)

My results = {'a': 400, 'b': 400}