> jeethu@dev:cpython  (3.7_list_insert_memmove)$ ./python -m timeit -s "l = []" "for _ in range(100): l.insert(0, None)"

Please don't use timeit, but perf timeit to run such *microbenchmark* (time smaller than 1 ms).

Your benchmark measures also the performance of the loop, it might be significant in such short loop (100 items). You may try to unroll the loop manually, and truncate the list:

vstinner@apu$ python3 -c 'print("l.insert(None); " * 3 + "l.clear();")'
l.insert(None); l.insert(None); l.insert(None); l.clear();

Example:

python3 -m perf timeit -s 'l=[]' $(python3 -c 'print("l.insert(0, None); " * 100 + "l.clear();")') --duplicate 100


Jeethu Rao: Are you using CPU isolation? What is your OS?