How come I need to use the copy module to copy a mutable data structure?

Question

I realized(the hard way) that to create copies of mutable data structures you can't just do this:
a = [1,2,3,4]
b = a
You have to do this:
import copy
a = [1,2,3,4]
b = copy.deepcopy(a)

Why do I have to do that.

Answer 1

A real good answer can be found here:

https://www.geeksforgeeks.org/copy-JUMP_LINK__&&__python__&&__JUMP_LINK-deep-copy-shallow-copy/

Answer 2

Huh. Never used that. I just do

b = a[:]

Answer 3

Choe
Wow. I never would have guessed.
Thanks.