dictionary merging test

test.py

from collections import defaultdict
import time


i = 100
for _ in range(3):
    list_of_dictionaries = [{1: 1} for i in range(i)]
    list_of_dictionaries.append(dict.fromkeys(range(i)))

    n = sum(map(len, list_of_dictionaries))
    m = len(set().union(*list_of_dictionaries))
    k = len(list_of_dictionaries)
    km = k * m

    print(f'\n\nn = {n}, m = {m}, k = {k}, km = {k * m}')

    print('\ndefaultdict')
    start = time.perf_counter()
    dd = defaultdict(list)
    for d in list_of_dictionaries:
        for k, v in d.items():
            dd[k].append(v)
    dt = time.perf_counter() - start

    print(f'time per n: {dt / n:0.12f}')
    print(f'time per km: {dt / km:0.12f}')

    print('\ncomprehension')

    start = time.perf_counter()
    allkeys = set().union(*list_of_dictionaries)

    res = {k: [d[k] for d in list_of_dictionaries if k in d] for k in allkeys}
    dt = time.perf_counter() - start

    print(f'time per n: {dt / n:0.12f}')
    print(f'time per km: {dt / km:0.12f}')

    i = i * 10