How do you check whether a number is divisible by another number?
integer, modulo, python
Solution
You do this using the modulus operator, `%`
n % k == 0
evaluates true if and only if `n` is an exact multiple of `k`. In elementary maths this is known as the remainder from a division.
In your current approach you perform a division and the result will be either
- always an integer if you use integer division, or
- always a float if you use floating point division.
It's just the wrong way to go about testing divisibility.
Problem
I need to test whether each number from 1 to 1000 is a multiple of 3 or a multiple of 5. I tried this code in Python 2.x: ``` n = 0 s = 0 while (n < 1001): x = n/3 if isinstance(x, (int, long)): print 'Multiple of 3!' s = s + n if False: y = n/5 if isinstance(y, (int, long)): s = s + n print 'Number: ' print n print 'Sum:' print s n = n + 1 ``` The idea is to try dividing the number and see if the result is an integer. However, I'm not getting the expected result. How do I test whether the number is an integer? In 2.x, division like this will produce an integer, discarding the remainder; see How can I force division to be floating point? Division keeps rounding down to 0? for details. In 3.x, the division will produce a floating-point value; the result is not "an integer" even if it is a whole number, so the `isinstance` check will fail. See Why does integer division yield a float instead of another integer? for details. If you need the remainder from integer division rather than just testing for divisibility, see Find the division remainder of a number.