copier vs deepcopy: What are the differences?

Key Differences Between Copier and Deepcopy

Copier and deepcopy are both functions in Python that are used to create copies of objects. However, they have some key differences in their functionality. Here are the main distinctions between the two:

1. Reference vs. New Object: When using the copier function, a new object is created that references the original object. This means that any changes made to the copied object will also affect the original object. In contrast, the deepcopy function creates a completely new and independent object with its own separate memory allocation. Any modifications made to the copied object will not affect the original object.

2. Shallow Copy vs. Deep Copy: Copier performs a shallow copy, which means that it only copies the top-level structure of an object and its reference to nested objects. If the original object contains any mutable objects, such as lists or dictionaries, only the references to these objects are copied. This means that changes made to the nested objects in the copied object will also affect the original object. On the other hand, deepcopy performs a deep copy, which means that it recursively copies all objects that are referenced within the original object, including the nested objects. In this way, deepcopy creates a completely independent replica of the original object.

3. Memory Efficiency: Copier is more memory-efficient compared to deepcopy because it does not create new objects for nested mutable objects. Instead, it simply references the original objects. This can be advantageous when dealing with large and complex data structures. Deepcopy, on the other hand, creates entirely new objects for any nested mutable objects, which may consume more memory, particularly if the object hierarchy is extensive.

4. Time Complexity: The time complexity of copier is O(1) as it only creates a new reference to the original object, regardless of the size of the object. In contrast, the time complexity of deepcopy is generally higher. It depends on the size and complexity of the object hierarchy that needs to be duplicated. Thus, deepcopy may take more time to complete, especially for large and deeply nested data structures.

5. Object Identity: When using copier, the copied object retains the same object identity as the original object, meaning that they are considered equal when using the '==' operator. In contrast, deepcopy generates a new object with a different object identity, so the copied object will not be considered equal to the original object when using the '==' operator.

6. Customization: Copier function does not provide much customization options for copying objects. It performs a straightforward shallow copy of the object. On the other hand, deepcopy offers more customization possibilities through the use of the __deepcopy__() method. By implementing this method in custom classes, you can define how the object should be deep copied.

In summary, copier creates a shallow copy of an object that references the original object, while deepcopy creates a deep copy that duplicates the original object and all its nested objects. Copier is more memory-efficient and has a faster time complexity, but changes to the copied object will also affect the original object. Deepcopy, on the other hand, creates an independent replica and does not alter the original object. Furthermore, deepcopy allows for more customization options through the __deepcopy__() method.