In [1]:

    

import itertools


    

In [2]:

    

l_2d_5 = [[0, 1, 2]] * 5
print(l_2d_5)


    

    




[[0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2], [0, 1, 2]]

In [3]:

    

%%timeit
list(itertools.chain.from_iterable(l_2d_5))


    

    




711 ns ± 21.2 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

In [4]:

    

%%timeit
sum(l_2d_5, [])


    

    




448 ns ± 10.8 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

In [5]:

    

l_2d_100 = [[0, 1, 2]] * 100


    

In [6]:

    

%%timeit
list(itertools.chain.from_iterable(l_2d_100))


    

    




7.27 µs ± 390 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

In [7]:

    

%%timeit
sum(l_2d_100, [])


    

    




41 µs ± 1.34 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

In [8]:

    

l_2d_10000 = [[0, 1, 2]] * 10000


    

In [9]:

    

%%timeit
list(itertools.chain.from_iterable(l_2d_10000))


    

    




513 µs ± 15.5 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [10]:

    

%%timeit
sum(l_2d_10000, [])


    

    




418 ms ± 22.8 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)