Dividing, and what is left over

Here is the surprise. Even when it divides exactly, / gives you a .0 on the end.

10 / 2 shows up as 5.0, not 5. Python has decided that the moment you use / you are in the world of decimals.

Try something like 10 / 3 and the decimals run on and on.

A computer can only hold so many digits of a decimal, so the tail end sometimes stops on an odd-looking digit instead of a neat 3. That is not a bug, that is just how it is.

Two slashes together, //, throw away everything after the decimal point.

Use it when what you want is a count — "10 sweets shared between 3 people, how many each?"

% gives you the remainder. In that same example, it is how many sweets are still in the bag once you have handed them out.

% is the per cent sign, but in Python it means remainder. Completely different job, so watch out for that.

Same "10 divided by 3", but the symbol changes with what you want to know.

• 10 / 3 … the exact answer → 3.3333333333333335
• 10 // 3 … how many fit → 3
• 10 % 3 … what is left → 1

% turns up a lot from here on. It is how you check whether a number is even, or a multiple of three.