python - Why does a[0] change?

Question

This question already has answers here:

List changes unexpectedly after assignment. Why is this and how can I prevent it? (22 answers)

Changing one list unexpectedly changes another, too [duplicate] (5 answers)

Closed 5 years ago.

When I do:

a = [7,3,4]
b = a
b[0] = 10

b[0] is of course set to 10, but a[0] is also set to 10. Why is this?

Answer 1

b = a

This makes b and a reference to the same list object. If you want b to reference to a new list object that is a copy of a, try:

b = a[:]