Python Shallow vs Deep Copy

"""
1. Copy by Reference
2. Shallow Copy
3. Deep Copy
"""

import copy

#Copy Ref
old_list = [[1, 2, 3], [4, 5, 6], [7, 8, 'a']]
new_list = old_list
new_list[2][2] = 9

print('----------')
print('ID of Old List:', id(old_list))
print('ID of New List:', id(new_list))
print('Copy Ref - Old List:', old_list)
print('Copy Ref - New List:', new_list)
print('----------')

#Output
#ID of Old List: 140672073880512
#ID of New List: 140672073880512
#Copy Ref - Old List: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
#Copy Ref - New List: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]


#Shallow Copy

##############
#A shallow copy creates a new object which stores the reference of the original elements.
old_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
new_list = copy.copy(old_list)

print("Shallow Copy Old list:", old_list)
print("Shallow Copy New list:", new_list)
print('----------')

#Output:
#Shallow Copy Old list: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
#Shallow Copy New list: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

#Shallow Copy - append

######################

old_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
new_list = copy.copy(old_list)
new_list.append([10,11,12])
print("Shallow Copy add Old list:", old_list)
print("Shallow Copy add New list:", new_list)
print('----------')

#Output:
#Shallow Copy add Old list: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
#Shallow Copy add New list: [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]


#Shallow Copy - nested update

###########################
#Existing elements will get updated - since it has reference to original elements
old_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
new_list = copy.copy(old_list)
new_list[1][1] = 400
print("Shallow Copy nested Old list:", old_list)
print("Shallow Copy nested New list:", new_list)
print('----------')

#Output:
#Shallow Copy nested Old list: [[1, 2, 3], [4, 400, 6], [7, 8, 9]]
#Shallow Copy nested New list: [[1, 2, 3], [4, 400, 6], [7, 8, 9]]


#Deep Copy###########
#It makes complete copy of elements
old_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
new_list = copy.deepcopy(old_list)
new_list[1][1] = 400
print('ID of Old List:', id(old_list))
print('ID of New List:', id(new_list))

print("Deep Copy Old list:", old_list)
print("Deep Copy New list:", new_list)

#Output:
#ID of Old List: 140672073879792
#ID of New List: 140672073880992
#Deep Copy Old list: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
#Deep Copy New list: [[1, 2, 3], [4, 400, 6], [7, 8, 9]]