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

I've recently started using Python and this "feature" baffled me. Although there are many answers given, I'll post my understanding anyway.

If I want to swap the values of two variables, in JavaScipt, I'd do the following:

var a = 0;
var b = 1;

var temp = a;
a = b;
b = temp;

I'd need a third variable to temporarily hold one of the values. A very straightforward swap wouldn't work, because both of the variables would end up with the same value.

var a = 0;
var b = 1;

a = b; // b = 1 => a = 1
b = a; // a = 1 => b = 1

_{Imagine having two different (red and blue) buckets and having two different liquids (water and oil) in them, respectively. Now, try to swap the buckets/liquids (water in blue, and oil in red bucket). You can't do it unless you have an extra bucket.}

Python deals with this with a "cleaner" way/solution: Tuple Assignment.

a = 0
b = 1

print(a, b) # 0 1

# temp = a
# a = b
# b = temp

a, b = b, a # values are swapped

print(a, b) # 1 0

I guess, this way Python is creating the "temp" variables automatically and we don't have to worry about them.