pre_allocate_list.py

def append_to_list(size=1000000):
    result = []
    for i in range(size):
        result.append(1)

def fill_pre_allocated_list(size=1000000):
    result = size * [None]
    for i in range(size):
        result[i]= 1
        
%timeit append_to_list()
# 10 loops, best of 3: 150 ms per loop
%timeit fill_pre_allocated_list() 
# 10 loops, best of 3: 111 ms per loop