python list.pop() modifies original list (not just copy)

Question

Situation: After making a copy of the original list I use pop to modify said copy. As it turns out, the original list gets affected by the change.

I even after check

Answer 1

some_list[:] is only a shallow copy. You seem to need a deep copy

from copy import deepcopy

copy = deepcopy(some_list)

Edit

To understand why "one objects affects the other" take a look at the id of each list:

original = [[1, 2], [3, 4]]
shallow = original[:]
deep = deepcopy(original)

print([id(l) for l in original])
# [2122937089096, 2122937087880]

print([id(l) for l in shallow])
# [2122937089096, 2122937087880]

print([id(l) for l in deep])
# [2122937088968, 2122937089672]

You can see that the ids of the lists in original are the same as the ids in shallow. That means the nested lists are the exact same objects. When you modify one nested list the changes are also in the other list.

The ids for deep are different. That are just copies. Changing them does not affect the original list.