How to Create Truly Independent Copies of Python Lists?

Creating Unmodifiable Clones of Python Lists

When assigning new_list to my_list, it's not an actual separate list creation. Instead, it's just a reference pointing to the same list, causing any changes in new_list to be reflected in my_list.

Copying Lists Effectively

To avoid unexpected list modifications, several methods exist for list cloning:

• list.copy() Method: (Python 3.3 ):

new_list = old_list.copy()

• Slicing:

new_list = old_list[:]

• list() Constructor:

new_list = list(old_list)

• copy.copy() Function:

import copy
new_list = copy.copy(old_list)

• copy.deepcopy() Function: (Copies nested elements recursively)

import copy
new_list = copy.deepcopy(old_list)

Example:

class Foo:
    def __init__(self, val):
        self.val = val

foo = Foo(1)

a = ['foo', foo]
b = a.copy()
c = a[:]
d = list(a)
e = copy.copy(a)
f = copy.deepcopy(a)

a.append('baz')
foo.val = 5

print(f'original: {a}\nlist.copy(): {b}\nslice: {c}\nlist(): {d}\ncopy: {e}\ndeepcopy: {f}')

Output:

original: ['foo', Foo(5), 'baz']
list.copy(): ['foo', Foo(5)]
slice: ['foo', Foo(5)]
list(): ['foo', Foo(5)]
copy: ['foo', Foo(5)]
deepcopy: ['foo', Foo(1)]

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