# Fix Python – How do you check whether a number is divisible by another number?

## Question

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.

Now we will see solution for issue: How do you check whether a number is divisible by another number?

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.

This question is answered By – David Heffernan