What is shallow copying?

Shallow copy creates a new complex object but does not create copies of the nested objects within it. Instead, it copies references to the nested objects of the original object.

Main points:

• Creates a new collection (list, dictionary, set).
• Elements of the new collection are references to the same objects as those in the original collection.
• Modifying nested objects in one copy will reflect in the other.
• Modifying the collection itself (adding/removing elements) in one copy will not affect the other.

Implementations:

• .copy() method for lists, dictionaries, sets.
• copy.copy() function from the copy module.
• Slice method [:] for lists.

# Example with list
original_list = [[1, 2], 3]
shallow_copy_list = original_list.copy()

print(f"Original: {original_list}")
print(f"Shallow copy: {shallow_copy_list}")
print(f"Identity of nested lists: {original_list[0] is shallow_copy_list[0]}") # True - references are the same

original_list[0][0] = 99 # Changing nested list

print(f"After change original: {original_list}")
print(f"After change shallow copy: {shallow_copy_list}") # Change is visible in both copies

original_list.append(4) # Changing the collection itself

print(f"After append original: {original_list}")
print(f"After append shallow copy: {shallow_copy_list}") # Change only in original

# Example with copy.copy()
import copy

original_dict = {'a': [1, 2], 'b': 3}
shallow_copy_dict = copy.copy(original_dict)

print(f"Original: {original_dict}")
print(f"Shallow copy: {shallow_copy_dict}")
print(f"Identity of nested lists: {original_dict['a'] is shallow_copy_dict['a']}") # True

original_dict['a'][0] = 99 # Changing nested list

print(f"After change original: {original_dict}")
print(f"After change shallow copy: {shallow_copy_dict}") # Change is visible in both copies