Which is faster: x*x or x**2?

python performance mathematical-optimization cpu-speed
kmonsoor picture kmonsoor · Dec 25, 2013 · Viewed 11.3k times · Source

I am trying to optimize my Python code. Between:

y = x*x

or

y = x**2

if I need one trillion iterations in a speed-critical program, which one should I choose?

Answer

gthacoder picture gthacoder · Dec 25, 2013

x**2 is faster than x*x.

Implementation of exponent has some overhead in Python, so it is usually faster to use your custom multiplication O(n) with small multiplication count. x*x*x*x*x is way faster than x**5. Exponent time is a sort of constant. Your multiplication time is increasing with exponent parameter, so with a large parameter it is better to use exponent. However, with really very small parameter (2, in your case), exponent is faster than multiplication. And x**2 is faster than x*x, although x**3 is way slower than x*x*x. You can find a nice benchmark in this answer.

Related questions

Fastest way to check if a value exists in a list

What is the fastest way to know if a value exists in a list (a list with millions of values in it) and what its index is? I know that all values in the list are unique as in this …

Read More
How to measure elapsed time in Python?

What I want is to start counting time somewhere in my code and then get the passed time, to measure the time it took to execute few function. I think I'm using the timeit module wrong, but the docs are …

Read More
String formatting: % vs. .format vs. string literal

Python 2.6 introduced the str.format() method with a slightly different syntax from the existing % operator. Which is better and for what situations? Python 3.6 has now introduced another string formatting format of string literals (aka "f" strings) via the syntax f"…

Read More