in C as much as possible In [29]: In [31]: numbers = range(1000) % timeit [x*2 for x in numbers] import numpy as np numbers = np.arange(1000) % timeit numbers*2 10000 loops, best of 3: 47.1 µs per loop The slowest run took 17.59 times longer than the fastest. This could mean that an intermediate result is being cached. 1000000 loops, best of 3: 1.48 µs per loop