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

The first expression:

1. Creates a temporary tuple with value y,x+y
2. Assigned in to another temporary tuple
3. Extract the tuple to variables x and y

The second statement is actually two expressions, without the tuple usage.

The surprise is, the first expression is actually:

temp=x
x=y
y=temp+y

You can learn more about the usage of comma in "Parenthesized forms".