List operators

Question

a = [1, 2, 3]
b = a
b[0] = 3
print(a)

output is 3, 2, 3

why is a here behaving like b?

with integers it works fine:
a = 1
b = a
b = 2
print(a)
output is 1

Answer 1

This is how lists work in Python. Instead of being just a collection of values, they should be regarded as pointers to memory addresses where those values are stored.
So assigning a variable to a list like you did makes both point to the same addresses. If a value is changed there, both pointers get changed.

In order to make a "copy" of a list, you should use the following syntax:
b = a[::]
That shall produce a slice of a and attribute it to b. Since the slice will be equal to the whole length of a list, you will effectively get a copy of a at b.

Answer 2

output should be 3,2,3