如何在python中的不同字典中添加相同键的值？

Question

I have something like this:

A = {"Green":{"Small": 5, "Medium": 10, "Large": 15}, "Yellow": {"Small": 7, "Medium": 14, "Large": 21}}

B = {"Green":{"Small": 1, "Medium": 2, "Large": 3}, "Yellow": {"Small": 3, "Medium": 6, "Large": 9}}

I want to write a function to get a dictionary "C" like this:

C = {"Green":{"Small": 6, "Medium": 12, "Large": 18}, "Yellow": {"Small": 10, "Medium": 20, "Large": 30}}

Which is just the sum of each value for it's key (which is the same in all dictionaries. Right now my "solution" is way too long and certainly not elegant. Can anyone give me some pointers on how I can make a relatively short function to achieve this?

Answer 1

Good old loops:

C = {}
for k, v in A.items():
    inner = {}
    for inner_k, inner_v in v.items():
        inner[inner_k] = inner_v + B[k][inner_k]
    C[k] = inner

>>> C
{'Green': {'Large': 18, 'Medium': 12, 'Small': 6},
 'Yellow': {'Large': 30, 'Medium': 20, 'Small': 10}}

Answer 2

A function which takes an arbitrary number of dictionaries in the form OP describes:

from pprint import pprint

def dsum(*args):
    return {
        k1: {
            k: sum(d.get(k1, dict()).get(k, 0) for d in args)
            for k in set.union(*(set(d.get(k1, dict())) for d in args))
        }
        for k1 in set.union(*(set(d) for d in args))
    }

A = {"Green":{"Small": 5, "Medium": 10, "Large": 15}, "Yellow": {"Small": 7, "Medium": 14, "Large": 21}}

B = {"Green":{"Small": 1, "Medium": 2, "Large": 3}, "Yellow": {"Small": 3, "Medium": 6, "Large": 9}}

C = {"Green":{"Small": 6, "Medium": 12, "Large": 18}, "Yellow": {"Small": 10, "Medium": 20, "Large": 30}}

testC = dsum(A, B)
assert C == testC
pprint(testC)

Answer 3

C={k: {kk: v + B[k][kk] for kk, v in a.items()} for k, a in A.items()}

在 python2 中更喜欢.iteritems()

Answer 4

A solution for missing keys:

def merge_by_addition(d1, d2):
    def m2(d1_, d2_):
        keys_ = set(d1_.keys()) | set(d2_.keys())
        return {k_: (d1_.get(k_, 0) + d2_.get(k_, 0)) for k_ in keys_}
    keys = set(d1.keys()) | set(d2.keys())
    return {k: m2(d1.get(k, {}), d2.get(k, {})) for k in keys}