What is the difference between a shallow copy and a deep copy of a nested list with nested mutable elements in Python using recursion?
Richard W

In Python, when dealing with nested lists that contain mutable elements (such as other lists), you have the option to create shallow copies or deep copies. The difference between the two lies in how they handle the references to the nested mutable elements. Let's explore the concepts of shallow copy and deep copy using recursion: 1. Shallow Copy: - A shallow copy creates a new list object but references the same nested mutable elements as the original list. - If you modify one of the nested mutable elements in the shallow copy, the change will be reflected in the original list as well. - Shallow copy is performed using thecopy module or the list's slicing notation[:]. Here's an example that demonstrates shallow copy using recursion:

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   import copy
   
   original_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   
   shallow_copy = copy.copy(original_list)
   # Or: shallow_copy = original_list[:]
   
   # Modifying a nested element in the shallow copy
   shallow_copy[0][0] = 10
   
   print(original_list)  # Output: [[10, 2, 3], [4, 5, 6], [7, 8, 9]]
   print(shallow_copy)   # Output: [[10, 2, 3], [4, 5, 6], [7, 8, 9]]

In the example, modifying the value10 in the shallow copy's nested list also affects the original list. This behavior occurs because both the original list and the shallow copy reference the same nested mutable elements. 2. Deep Copy: - A deep copy creates a completely independent copy of the original list and its nested mutable elements. - If you modify a nested mutable element in the deep copy, the original list remains unchanged. - Deep copy is performed using thecopy module. Here's an example that demonstrates deep copy using recursion:

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   import copy
   
   original_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   
   deep_copy = copy.deepcopy(original_list)
   
   # Modifying a nested element in the deep copy
   deep_copy[0][0] = 10
   
   print(original_list)  # Output: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   print(deep_copy) # Output: [[10, 2, 3], [4, 5, 6], [7, 8, 9]]

In this example, modifying the value10 in the deep copy's nested list does not affect the original list. The deep copy creates a new list object with its own independent copies of the nested mutable elements. When working with nested lists that contain mutable elements, it's important to consider whether you need a shallow copy or a deep copy based on your specific requirements. Shallow copy provides a more lightweight approach as it shares references, while deep copy ensures complete independence but may be less efficient for large and complex data structures.

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