Variable assignment query in python

Question

I am writing Fibonacci code in python. The below solution is mine.

While the other below solution is from python.org.

Can anyone tell me why it yields a different answer even though the logic of assigning the variables is the same?

Answer 1

The lines

a = b # Assigns the value of 'b' to 'a'
b = a + b # Adds the new value of 'a' to 'b'

whereas,

a, b = b, a+b Assigns the value of b to a. Adds the existing value of a to b.

Answer 2

Those two programs are not equivalent. The right hand side of the equals (=) is evaluated all together. Doing:

a=b
b=a+b

Is different from:

a,b = b,a+b

This is in reality the same as:

c = a
a = b
b = b + c

Your example is actually covered on the Python documentation:

The first line contains a multiple assignment: the variables a and b simultaneously get the new values 0 and 1. On the last line this is used again, demonstrating that the expressions on the right-hand side are all evaluated first before any of the assignments take place. The right-hand side expressions are evaluated from the left to the right.