Adirio

import random
import timeit

t1 = [[random.randint(-100, 100), 0] for n in range(10000)]
t2 = [[random.randint(-100, 100), 0] for n in range(10000)]

print('{:^24} | {:^24}'.format('Dict unpacking', 'List concat'))
for i in range(10):
  s1 = timeit.timeit('d = {**dict(t1), **dict(t2)}', number=1000, globals= globals())
  s2 = timeit.timeit('d = dict(t1 + t2)', number=1000, globals= globals())