Group by multiple keys and summarize/average values of a list of dictionaries

Question

What is the most pythonic way to group by multiple keys and summarize/average values of a list of dictionaries in Python please? Say I have a list of dictionaries as below:<

Answer 1

Like always there are lots of valid solutions, I like the defaultdict one, since I find it easier to understand.

from collections import defaultdict as df
food = df(lambda:df(lambda:df(int)))
for dct in input:  food[dct['transId']][dct['sku']][dct['dept']]=dct['qty']
output_tupl=[(d1,d2,sum(food[d1][d2][d3] for d3 in food[d1][d2]) )for d1 in food for d2 in food[d1]]