Question

I am new to Python (and dont know much about programming anyway), but I remember reading that python generally does not copy values so any statement a = b makes b point to a. If I run

a = 1
b = a
a = 2
print(b)

gives the result 1. Should that not be 2?

Answer 1

No, the result should be 1.

Think of the assignment operator (=) as the assignment of a reference.

a = 1  # a references the integer object 1
b = a  # b and a reference the same object
a = 2  # a now references a new object (2)
print b  # prints 1 because you changed what a references, not b

This whole distinction really is most important when dealing with mutable objects such as lists as opposed to immutable objects like int, float and tuple.

Now consider the following code:

a = []  # a references a mutable object
b = a   # b references the same mutable object
b.append(1)  # change b a little bit
print a  # [1] -- because a and b still reference the same object 
         #        which was changed via b.