• author: Python and Pandas with Reuven Lerner

Understanding How to Copy Lists in Python

Welcome back to our video explainer of the Python standard library. In this segment, we will dive into the topic of how to copy a list in Python.

Let's start off by considering the following list:

my_list = [10, 20, 30, 40, 50]

To copy this list, we cannot simply say x = my_list. Doing so creates another reference to the same list rather than a new copy of the list.

Shallow Copy

A shallow copy is one that copies the references to the objects in the original list into the new list. This means that when the original list is changed, the copied elements are also affected.

One way to obtain a shallow copy is to use slicing. For example:

x = my_list[:]

Another way to get a shallow copy is using the copy() method. Starting with Python 3.7, this method is available for lists.

x = my_list.copy()

It is important to note that a shallow copy works well when the elements in the list are immutable, such as numbers, strings, and tuples. However, for mutable objects, such as lists, sets, and dictionaries, a deep copy is required to avoid unwanted changes to the copied elements.

Deep Copy

A deep copy creates a new list with new objects, recursively copying all the objects in the original list. This means that the copy is completely independent of the original list, and changes made to one list do not affect the other.

To get a deep copy of a list, we need to use the deepcopy() function from the copy module in the standard library.



To summarize, there are two types of copying methods available for lists in Python:

  • Shallow Copy: This method copies the references to the original objects in the new list. It is sufficient for copying lists with immutable elements.
  • Deep Copy: This method creates a completely new list with new objects, recursively copying all the objects in the original list. It is required for copying lists with mutable elements.

Make sure to choose the appropriate method for your use case to avoid unintended consequences. Remember to use copy() for shallow copying and deepcopy() for deep copying mutable objects.

Stay tuned for more useful tips and tricks on the Python standard library! Don't forget to subscribe and share with your friends.

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