Source code available on GitHub.
This first problem gets us off to an easy start. It asks:
We want to iterate through all the numbers below 1000, so we’ll use a for loop:
for i in range(1,1000):
This tells Python to start with i=1 and keep incrementing i every loop up until i=999. The easiest way to check for divisibility is with the modulus operator, %. Writing x % y returns the value of 
– that is, the remainder when dividing 
by 
.
So, using an if statement, we write
if i % 3 == 0 or i % 5 == 0:
which will return true when the number is a multiple of (had zero remainder when divided by) either 3 or 5. If this happens, we want to add i to some sum so that when the for loop terminates, that value is our final value. We’ll call it running_sum.
Lastly, we want to print the result. Here’s the final code:
running_sum = 0
for i in range(1,1000):
if i % 3 == 0 or i % 5 == 0:
running_sum += i
print(running_sum)