Multiple assignment and evaluation order in Python

Question

What is the difference between the following Python expressions:

# First:

x,y = y,x+y

# Second:

x = y
y = x+y

First gives diffe

Answer 1

Other answers have already explained how it works, but I want to add a really concrete example.

x = 1
y = 2
x, y = y, x+y

In the last line, first the names are dereferenced like this:

x, y = 2, 1+2

Then the expression is evaluated:

x, y = 2, 3

Then the tuples are expanded and then the assignment happens, equivalent to:

x = 2; y = 3