What does this expression do: (x, y) = (y, x % y)?

Question

I see below code but do not know what does it do.

(x, y) = (y, x % y)

At the beginning I thought it does below:

x=y
y=x%y

But I noticed I am not right. Can someone explain what (x, y) = (y, x % y) does?

Answer 1

It's called tuple assignment/unpacking, and to reproduce it linearly, you need a temporary location to store the value of x.

It is more equivalent to:

temp=x
x=y
y=temp%y