Difference between Deep copy and shallow copy in python

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<<–2/”>a href=”https://exam.pscnotes.com/5653-2/”>p>nuances of deep copy and shallow copy in Python.

Introduction

In Python, copying objects isn’t always straightforward. When dealing with mutable objects (like lists, dictionaries, or custom classes), the way you copy them determines whether changes in one object affect others. This is where the concepts of deep copy and shallow copy become crucial.

Key Differences: Deep Copy vs. Shallow Copy

Feature Shallow Copy Deep Copy
Creation copy.copy(x) or slicing (x[:]) copy.deepcopy(x)
Memory Allocation Creates a new object but references the same nested objects as the original. Creates a completely new object with independent copies of all nested objects.
Effect of Changes Modifying nested objects in the copy affects the original and vice versa. Modifying nested objects in the copy does not affect the original, and vice versa.
Use Cases Suitable when you want changes to the copy to reflect in the original and vice versa. Suitable when you need a truly independent copy where changes in one don’t affect the other.
Speed Faster, as it only creates a new object and copies references. Slower, especially with deeply nested structures, as it recursively copies all objects.

Advantages and Disadvantages

Shallow Copy

  • Advantages:
    • Faster execution due to simpler operations.
    • Memory efficient when you only need to duplicate the structure, not the data.
  • Disadvantages:
    • Can lead to unintended side effects if nested objects are modified.
    • Not suitable for creating completely independent copies.

Deep Copy

  • Advantages:
    • Creates truly independent copies, isolating changes to the copied object.
    • Safer for complex data structures with nested mutable objects.
  • Disadvantages:
    • Can be significantly slower for large or deeply nested objects.
    • Consumes more memory as it duplicates all data.

Similarities

  • Both shallow copy and deep copy create a new object that is distinct from the original.
  • Both are used to duplicate objects in Python.
  • Both are available in the copy module.

FAQs

Q: When should I use a shallow copy?

A: Use shallow copy when:
* You’re working with simple objects or immutable objects (like numbers, strings, or tuples).
* You intentionally want changes in the copy to affect the original.

Q: When should I use a deep copy?

A: Use deep copy when:
* You have complex objects with mutable nested objects (like lists or dictionaries).
* You need complete independence between the original and the copy.

Q: Can I customize the behavior of deep copy for my classes?

A: Yes, you can define the __deepcopy__ method in your class to control how deep copying is performed for your objects.

Q: Are there any alternatives to deep copy?

A: Yes, consider these alternatives:
* Serialization: Convert the object to a byte stream (e.g., using pickle) and then deserialize it to create a new, independent copy.
* Manual Copying: Write custom code to recursively copy each element of the object. This gives you full control but can be error-prone.

Example

import copy

original_list = [[1, 2], [3, 4]]
shallow_copy = copy.copy(original_list)
deep_copy = copy.deepcopy(original_list)

shallow_copy[0][0] = 99
deep_copy[0][0] = 88

print("Original:", original_list)    # Output: [[99, 2], [3, 4]]
print("Shallow:", shallow_copy)      # Output: [[99, 2], [3, 4]]
print("Deep:", deep_copy)            # Output: [[88, 2], [3, 4]]

In this example, modifying the nested list in the shallow copy also modifies the original list, while the deep copy remains unaffected.

Feel free to ask if you have more questions or want to explore specific scenarios!

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