Background

I noticed a difference in speed when inserting an element to the beginning of the list using list.insert vs list slice assignment. Upon inspecting the code, the usage of memmove in the list slice assignment code seems to be the providing a slight speed boost over the for loop used in the list.insert implementation.

The following code was used to benchmark the difference:

import random
import timeit

runs = 100000
setup = 'import random;lst=[random.randrange(100000) for _ in range(100000)]; x = random.randrange(100000)'

print(timeit.timeit(stmt='lst[:0] = [x]', setup=setup, number=runs))
print(timeit.timeit(stmt='lst.insert(0, x)', setup=setup, number=runs))

Original:

Slice assignment: 7.394628149999335s
list.insert:      8.910868348000804s

Using memmove in list.insert():

Slice assignment: 7.252985826999065s
list.insert:      7.215608489997976s

(Compiled with optimizations and tested on Arch Linux, kernel 5.18)