Is divmod() faster than using the % and // operators?

Question

I remember from assembly that integer division instructions yield both the quotient and remainder. So, in python will the built-in divmod() function be better performance-wi

Answer 1

Martijn's answer is correct if you're using "small" native integers, where arithmetic operations are very fast compared to function calls. However, with bigints, it's a whole different story:

>>> import timeit
>>> timeit.timeit('divmod(n, d)', 'n, d = 2**74207281 - 1, 26', number=1000)
24.22666597366333
>>> timeit.timeit('n // d, n % d', 'n, d = 2**74207281 - 1, 26', number=1000)
49.517399072647095

when dividing a 22-million-digit number, divmod is almost exactly twice as fast as doing the division and modulus separately, as you might expect.

On my machine, the crossover occurs somewhere around 2^63, but don't take my word for it. As Martijn says, measure! When performance really matters, don't assume that what held true in one place will still be true in another.