Why does integer division return float?

Question

From what I understand, the integer division // operator is guaranteed to return an integer. However, while 2 // 1 == 1, I also get 2.0 // 1 == 2.0. Why doesn't python produce an integer, and, is it always safe to cast the output to int?

Answer 1

You misunderstood the operator. It is a floor division operator, not an integer division operator.

For floating point inputs, it'll still return a floored float value.

From the Binary arithmetic operations section:

The / (division) and // (floor division) operators yield the quotient of their arguments. The numeric arguments are first converted to a common type. Division of integers yields a float, while floor division of integers results in an integer; the result is that of mathematical division with the ‘floor’ function applied to the result.

The result of flooring is safe to convert to an integer.

Note that Python applies these rules to almost all numeric types when used in binary arithmetic operations, division and floor division are not exceptional here, nor is this specific to integers and floats (try it with import fractions then 2 // fractions.Fraction(1, 1) for example). The only exception here are complex numbers, for which floor division, modulo operator or divmod() are not defined.