How to merge multiple dicts with same key?

Question

I have multiple dicts/key-value pairs like this:

d1 = {key1: x1, key2: y1}  
d2 = {key1: x2, key2: y2}  

I want the result to be a new dict (in most efficient way, if possible):

d = {key1: (x1, x2), key2: (y1, y2)}  

Actually, I want result d to be:

d = {key1: (x1.x1attrib, x2.x2attrib), key2: (y1.y1attrib, y2.y2attrib)}  

If somebody shows me how to get the first result, I can figure out the rest.

Answer 1

Here's a general solution that will handle an arbitrary amount of dictionaries, with cases when keys are in only some of the dictionaries:

from collections import defaultdict

d1 = {1: 2, 3: 4}
d2 = {1: 6, 3: 7}

dd = defaultdict(list)

for d in (d1, d2): # you can list as many input dicts as you want here
    for key, value in d.items():
        dd[key].append(value)

print(dd)

Shows:

defaultdict(<type 'list'>, {1: [2, 6], 3: [4, 7]})

Also, to get your .attrib, just change append(value) to append(value.attrib)