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

In the second case, you assign x+y to x

In the first case, the second result (x+y) is assigned to y

This is why you obtain different results.

After your edit

This happen because, in the statement

x,y = y,x+y

all variables at the right member are evaluated and, then, are stored in the left members. So first proceed with right member, and second with the left member.

In the second statement

x = y
y = x + y

yo first evaluated y and assign it to x; in that way, the sum of x+y is equivalent to a sum of y+y and not of x+x wich is the first case.