Pthon deep copy

Shallow and deep copy operations

copy.copy(x)

Return a shallow copy of x.

copy.deepcopy(x)

Return a deep copy of x.

A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.

A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.

This behaviour is depicted in the following diagram: it is a shallow copy

 lst1 = ['a','b',['ab','ba']]
>>> lst2 = lst1[:]
>>> lst2[0] = 'c'
>>> lst2[2][1] = 'd'
>>> print(lst1)
['a', 'b', ['ab', 'd']]

The following diagram depicts what happens, if one of the elements of a sublist will be changed: Both the content of lst1 and lst2 are changed. 

from copy import deepcopy

lst1 = ['a','b',['ab','ba']]

lst2 = deepcopy(lst1)

lst2[2][1] = "d"
lst2[0] = "c";

print lst2
print lst1

If we save this script under the name of deep_copy.py and if we call the script with "python deep_copy.py", we will receive the following output:

$ python deep_copy.py 
['c', 'b', ['ab', 'd']]
['a', 'b', ['ab', 'ba']]