Shallow Copy
In Python, when we talk about copying objects, we often come across the terms «shallow copy» and «deep copy». These terms refer to different ways of creating copies of objects, and understanding the difference between them is crucial for writing efficient and bug-free code.
A shallow copy of an object is a new object that is created by copying the reference of the original object. In other words, both the original object and the shallow copy point to the same memory location. Any changes made to the original object will be reflected in the shallow copy, and vice versa.
To create a shallow copy of an object in Python, we can use the copy() method from the copy module or the copy() method of the object itself.
Deep Copy
On the other hand, a deep copy of an object is a new object that is created by recursively copying all the objects that are referenced by the original object. In other words, a deep copy creates a completely independent copy of the original object, including all its nested objects. Any changes made to the original object will not affect the deep copy, and vice versa.
To create a deep copy of an object in Python, we can use the deepcopy() method from the copy module or the copy.deepcopy() method of the object itself.
When to Use Shallow Copy
Shallow copy is useful when we want to create a new object that shares some or all of its data with the original object. This can be beneficial in terms of memory efficiency, as creating a shallow copy does not require duplicating the entire object and its nested objects.
For example, if we have a list of objects and we want to create a new list that contains the same objects, we can use shallow copy. Any changes made to the objects in the original list will be reflected in the new list, which can be useful in certain scenarios.
When to Use Deep Copy
Deep copy is useful when we want to create a completely independent copy of an object, including all its nested objects. This is necessary when we want to modify the copied object without affecting the original object or any other copies.
For example, if we have a complex data structure like a nested list or a dictionary, and we want to create a new copy that we can modify without affecting the original structure, we should use deep copy. Any changes made to the copied structure will not affect the original structure or any other copies.
Examples of Shallow Copy
Let’s take a look at some examples to better understand shallow copy in Python.
Example 1:
«`python
import copy
original_list = [1, 2, 3]
shallow_copy = copy.copy(original_list)
original_list.append(4)
print(original_list) # Output: [1, 2, 3, 4]
print(shallow_copy) # Output: [1, 2, 3, 4]
«`
In this example, we create a shallow copy of the original list using the copy() method from the copy module. Both the original list and the shallow copy point to the same memory location, so any changes made to the original list will be reflected in the shallow copy.
Example 2:
«`python
import copy
original_dict = {‘name’: ‘John’, ‘age’: 25}
shallow_copy = copy.copy(original_dict)
original_dict[‘age’] = 30
print(original_dict) # Output: {‘name’: ‘John’, ‘age’: 30}
print(shallow_copy) # Output: {‘name’: ‘John’, ‘age’: 30}
«`
In this example, we create a shallow copy of the original dictionary using the copy() method from the copy module. Both the original dictionary and the shallow copy point to the same memory location, so any changes made to the original dictionary will be reflected in the shallow copy.
Examples of Deep Copy
Now, let’s take a look at some examples to better understand deep copy in Python.
Example 1:
«`python
import copy
original_list = [1, 2, 3]
deep_copy = copy.deepcopy(original_list)
original_list.append(4)
print(original_list) # Output: [1, 2, 3, 4]
print(deep_copy) # Output: [1, 2, 3]
«`
In this example, we create a deep copy of the original list using the deepcopy() method from the copy module. The deep copy is completely independent of the original list, so any changes made to the original list will not affect the deep copy.
Example 2:
«`python
import copy
original_dict = {‘name’: ‘John’, ‘age’: 25}
deep_copy = copy.deepcopy(original_dict)
original_dict[‘age’] = 30
print(original_dict) # Output: {‘name’: ‘John’, ‘age’: 30}
print(deep_copy) # Output: {‘name’: ‘John’, ‘age’: 25}
«`
In this example, we create a deep copy of the original dictionary using the deepcopy() method from the copy module. The deep copy is completely independent of the original dictionary, so any changes made to the original dictionary will not affect the deep copy.
Conclusion
In conclusion, understanding the difference between shallow copy and deep copy in Python is essential for writing efficient and bug-free code. Shallow copy creates a new object that shares some or all of its data with the original object, while deep copy creates a completely independent copy of the original object, including all its nested objects.
Shallow copy is useful when we want to create a new object that shares data with the original object, while deep copy is useful when we want to create a completely independent copy of an object. By using the appropriate copy method, we can ensure that our code behaves as expected and avoids any unexpected side effects.
