When working with Python, understanding the difference between shallow copy and deep copy is crucial for efficiently handling objects, especially those with nested structures. In this Tutorialshore blog post, we’ll explore how these two types of copying differ and when to use each.
What is a Shallow Copy?
A shallow copy creates a new object but does not copy the objects contained within the original object. Instead, it copies references to these objects. This means that changes to the nested mutable objects in the shallow copy will also affect the original object, as they both share references to the same nested data.
Example:
import copy
original = [[1, 2, 3], [4, 5, 6]]
shallow = copy.copy(original)
# Modify the nested list
shallow[0][0] = 99
print("Original:", original) # Output: [[99, 2, 3], [4, 5, 6]] (original is affected)
Key Point:
- Only the outermost object is duplicated. The nested objects remain shared between the original and the copy.
What is a Deep Copy?
A deep copy, on the other hand, creates a new object and recursively copies all objects within the original. This ensures complete independence between the original and the copied object, even for deeply nested structures.
Example:
import copy
original = [[1, 2, 3], [4, 5, 6]]
deep = copy.deepcopy(original)
# Modify the nested list
deep[0][0] = 99
print("Original:", original) # Output: [[1, 2, 3], [4, 5, 6]] (original is unaffected)
Key Point:
- A deep copy duplicates everything, creating a fully independent replica.
Key Differences Between Shallow and Deep Copies
| Feature | Shallow Copy | Deep Copy |
|---|---|---|
| Outer object | New object is created. | New object is created. |
| Nested objects | References are copied. | Recursively duplicated. |
| Independence | Dependent on the original for nested objects. | Fully independent. |
| Use Case | Suitable for objects without nested mutable structures. | Suitable for complex, nested structures. |
When to Use Shallow Copy vs Deep Copy
- Shallow Copy is ideal when:
- You’re working with objects that don’t contain nested mutable objects.
- You want to avoid the overhead of recursively duplicating everything.
- Deep Copy is best when:
- You’re handling deeply nested objects where modifications should not affect the original.
- Complete independence between the original and the copied object is essential.
How to Create Copies in Python
Python’s copy module makes it easy to create both shallow and deep copies:
- Shallow Copy: Use
copy.copy(obj). - Deep Copy: Use
copy.deepcopy(obj).
Conclusion
Understanding the difference between shallow and deep copies can save you from unexpected bugs and improve the efficiency of your code. By knowing when to use each type of copy, you can better manage objects in Python and write more robust programs.
Experiment with these concepts and see how they apply to your projects!