This is one of the 100 recipes of the IPython Cookbook, the definitive guide to high-performance scientific computing and data science in Python.

# 4.1. Evaluating the time taken by a statement in IPython¶

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n = 100000

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%timeit sum([1. / i**2 for i in range(1, n)])

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%%timeit s = 0.
for i in range(1, n):
s += 1. / i**2

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import numpy as np

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%timeit np.sum(1. / np.arange(1., n) ** 2)


You'll find all the explanations, figures, references, and much more in the book (to be released later this summer).

IPython Cookbook, by Cyrille Rossant, Packt Publishing, 2014 (500 pages).