Python

When you're working with the binary representation of numbers.

In your code you had three numbers 25, 10 and 5. If we write those number in binary we get:

• 25: 0b00011001
• 10: 0b00001010
• 5: 0b00000101

(The 0b at the start is just a way of saying "this is binary")

When you do a bitwise-or, it's a bit like adding up but you don't bother with carrying anything. So let's do 25 | 10, starting at the right-hand end going bit by bit (bitwise):

• 0 | 1 = 1
• 1 | 0 = 1
• 0 | 0 = 0
• 1 | 1 = 1
• 1 | 0 = 1
• 0 | 0 = 0 for all the rest

So the result is 0b00011011 which is 27.

So now you're asking "when would I ever need to do such a thing?" and the flippant answer is "you'll know when you need it".

You're looking for more though, I know. Basically computers often put multiple bits of data into bitstreams (long sequences of bits). Think networking and file storage. Constructing these bitstreams is done with bitwise operators like |, &, ^, << and >>. Together they form a different type of maths to what you're used to.

These operators work in a very similar way to how +, -, * and / work. They take two numbers and return a third. If we rewrite your code using operators you're more familiar with...

    if coin == 25 | 10 | 5:  # if coin == 31
        ...
    if coin == 25 + 10 + 5:  # if coin == 40
        ...

...you can see it's obviously wrong because you're doing one comparison with the result of the operation (addition or bitwise-or), not three comparisons.