A Comprehensive Guide to Copying Arrays in Python

When working with arrays (or lists) in Python, it is essential to understand how to copy them properly. This knowledge ensures that changes made to the copied array do not affect the original array.

Key Concepts

• Shallow Copy vs. Deep Copy:
  • Shallow Copy: Creates a new object but inserts references to the objects found in the original.
  • Deep Copy: Creates a new object and recursively copies all objects found in the original.

Methods to Copy Arrays

1. Using the copy() Method

The copy() method creates a shallow copy of the list.

original_list = [1, 2, 3]
copied_list = original_list.copy()
copied_list[0] = 100

print(original_list)  # Output: [1, 2, 3]
print(copied_list)    # Output: [100, 2, 3]

2. Using List Slicing

You can create a copy by slicing the entire list.

original_list = [1, 2, 3]
copied_list = original_list[:]
copied_list[1] = 200

print(original_list)  # Output: [1, 2, 3]
print(copied_list)    # Output: [1, 200, 3]

3. Using the list() Constructor

The list() constructor can also be used to create a new list.

original_list = [1, 2, 3]
copied_list = list(original_list)
copied_list[2] = 300

print(original_list)  # Output: [1, 2, 3]
print(copied_list)    # Output: [1, 2, 300]

4. Using the copy Module for Deep Copy

For deep copying, use the copy module's deepcopy() function.

import copy

original_list = [[1, 2, 3], [4, 5, 6]]
copied_list = copy.deepcopy(original_list)
copied_list[0][0] = 100

print(original_list)  # Output: [[1, 2, 3], [4, 5, 6]]
print(copied_list)    # Output: [[100, 2, 3], [4, 5, 6]]

Conclusion

Understanding how to copy arrays in Python is crucial for effective data manipulation. Use the appropriate method based on whether you need a shallow copy or a deep copy to avoid unintentional changes to your original data.