salinan python vs deepcopy

For immutable objects, there is no need for copying because 
the data will never change, so Python uses the same data; 
ids are always the same. For mutable objects, 
since they can potentially change, [shallow] copy creates a new object.

Deep copy is related to nested structures. 
If you have list of lists, then deepcopy copies the nested lists also, 
so it is a recursive copy. With just copy, you have a new outer list, 
but inner lists are references.

Assignment (=) does not copy. It simply sets the reference to the old data. 
So you need copy to create a new list with the same contents.
Edi Sugiarto