How to combine (append values) two nested dictionaries with the same keys in python?

Question

dist = {'Berlin': {'Boston' : 6096.945, 'LA' : 9331.657, 'Chicago' : 7102.591},
        'Vienna': {'Boston' : 6508.405, 'LA' : 9841.482, 'Chicago' : 7560.970}, 
        'London': {'Boston' : 5484.658, 'LA' : 9383.686, 'Chicago' : 6741.855}}

time = {'Berlin': {'Boston' : 6, 'LA' : 9, 'Chicago' : 7},
        'Vienna': {'Boston' : 6, 'LA' : 9, 'Chicago' : 7}, 
        'London': {'Boston' : 5, 'LA' : 8, 'Chicago' : 6}}

How to merge two dictionaries to get values in a list as follows:

new_dict = {'Berlin': {'Boston' : [6096.95, 6], 'LA' : [9331.65, 9], 'Chicago' : [7102.59, 7]},
            'Vienna': {'Boston' : [6508.40, 6], 'LA' : [9841.48, 9], 'Chicago' : [7560.97, 7]}, 
            'London': {'Boston' : [5484.65, 5], 'LA' : [9383.68, 8], 'Chicago' : [6741.85, 6]}}

Thank you in advance!

Answer 1

You can solve that with a 2-level dict-comprehension

result = {
    city_from: {city_to: [distance_val, time[city_from][city_to]]
                for city_to, distance_val in cities_to.items()}
    for city_from, cities_to in dist.items()
}

Equivalent of a classic 2 for-loop solution

result = defaultdict(dict) # from collections import defaultdict
for city_from, cities_to in dist.items():
    for city_to, distance_val in cities_to.items():
        result[city_from][city_to] = [distance_val, time[city_from][city_to]]

Answer 2

Not too elegant, but works:

def combine_dicts(a, b):
    for key in b:
        if key in a:
            if isinstance(a[key], dict) and isinstance(b[key], dict):
                combine_dicts(a[key], b[key])
            else:
                a[key] = [a[key], b[key]]
        else:
            a[key] = [a[key], b[key]]
    return a

Note: this function will change the original dict a , if you wan't to leave the original dict unchanged, pass copies to func

from copy import deepcopy
combined = combine_dicts(deepcopy(dist), deepcopy(time))