preallocation_vs_listcomp.py

import matplotlib.pyplot as plt
import pandas as pd
from timeit import timeit

setup = """
def list_comp(d):
    return [ (x*2)/3 for x in d ]

def pre_allocate(d):
    result = [None]*len(d)
    for i, x in enumerate(d):
        result[i] = (x*2)/3
    return result

d = list(range({}))
"""

lc = [timeit("list_comp(d)", setup=setup.format(n), number=10) for n in N]
pa = [timeit("pre_allocate(d)", setup=setup.format(n), number=10) for n in N]

pd.DataFrame(dict(pre_allocate=pa, list_comp=lc), index=N).plot()
plt.savefig("pre-allocate-vs-list-comp.png")