If you want to make an independent copy of a compound object (list, dictionary, custom class instance) you should make use of deep copy, which:
- constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original;
- takes more time to complete, as there are many more operations to be performed;
- is implemented by the
deepcopy()function, delivered by the python 'copy' module
The general idea should be depicted like this:
A code creating an independent copy of the a_list object should look like the code presented in the right pane.
The graphical representation should look like the following:
The 'copy' module contains a function for shallow copying: copy(). Of course, you could say that for copying lists there is already the [:] notation, or a_list=list(b_list), and for dictionaries you could use a_dict = dict(b_dict).
But think about making use of polymorphism when you need a universal function to copy any type object, so that in that case using a copy() function is the smart way to accomplish the task.
Code
import copyprint("Let's make a deep copy")
a_list = [10, "banana", [997, 123]]
b_list = copy.deepcopy(a_list)
print("a_list contents:", a_list)
print("b_list contents:", b_list)
print("Is it the same object?", a_list is b_list)
print()
print("Let's modify b_list[2]")
b_list[2][0] = 112
print("a_list contents:", a_list)
print("b_list contents:", b_list)
print("Is it the same object?", a_list is b_list)