How to Copy a List in Python

Python is a popular and highly efficient programming language. One of the common tasks that you might need to perform in Python is copying a list. This might seem like a straightforward task, but it can get a bit complex due to the way Python handles objects and references. In this tutorial, we will guide you on how to copy a list in Python.

Step 1: Understanding Python Lists

In Python, lists are mutable objects. If you create a new variable and assign it to an existing list, the new variable will simply point to the same object. This means if you modify the new variable, the original list will be affected as well. This is called a shallow copy.

Step 2: The “=” Operator

The “=” operator creates a new reference to the same list. This is most commonly used to create a copy of a list. However, because this is a shallow copy, any changes made to the new list will also affect the original list.

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original_list = [1, 2, 3, 4, 5]
copied_list = original_list

Step 3: Using the copy() Method for a Shallow Copy

Python includes a list method called copy(). This method returns a new list that is a shallow copy of the original list.

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original_list = [1, 2, 3, 4, 5]
copied_list = original_list.copy()

Step 4: Using the list() Constructor for a Shallow Copy

You can also use the list() constructor to create a new list that is a copy of the original list. This is another method of performing a shallow copy.

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original_list = [1, 2, 3, 4, 5]
copied_list = list(original_list)

Step 5: Using the copy Module for a Deep Copy

If your list contains objects (like lists, custom objects, etc.) and you want to create a copy of the list and the objects it contains, you need a deep copy. For this purpose, Python provides the copy module which includes a function called deepcopy().

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

Full code:

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# Using copy.deepcopy() for complex lists
import copy
 
# Using "=" operator
original_list = [1, 2, 3, 4, 5]
copied_list = original_list
print(copied_list)
 
# Using copy() method
original_list = [1, 2, 3, 4, 5]
copied_list = original_list.copy()
print(copied_list)
 
# Using list() constructor
original_list = [1, 2, 3, 4, 5]
copied_list = list(original_list)
print(copied_list)
 
original_list = [1, 2, [3, 4], 5]
copied_list = copy.deepcopy(original_list)
print(copied_list)

Conclusion

Copying a list in Python can be accomplished in several ways. Depending on your specific needs, you may opt for shallow or deep copying. Understanding the difference, and when to use each method is crucial as you navigate Python’s list data structure.