Question

I came across this sample of code from a radix sort:

def getDigit(num, base, digit_num):
    # pulls the selected digit
    return (num // base ** digit_num) % base

What does the // do in Python?

Answer 1

// is the floor division operator. It produces the floor of the quotient of its operands, without floating-point rounding for integer operands. This is also sometimes referred to as integer division, even though you can use it with floats, because dividing integers with / used to do this by default.

In Python 3, the ordinary / division operator returns floating point values even if both operands are integers, so a different operator is needed for floor division. This is different from Python 2 where / performed floor division if both operands were integers and floating point division if at least one of the operands was a floating point value.

The // operator was first introduced for forward-compatibility in Python 2.2 when it was decided that Python 3 should have this new ability. Together with the ability to enable the Python 3 behavior via from __future__ import division (also introduced in Python 2.2), this enables you to write Python 3-compatible code in Python 2.