How to Copy List in Python

Python is a popular language that offers several data structures to store data. Lists are powerful python data structures that allow you to copy diverse data types in one place in a compact manner. They also offer many out-of-the-box functions. Sometimes you may need to copy lists in python. In this article, we will learn how to copy list in python.

How to Copy List in Python

In python, there are two ways to copy lists – deep copy and shallow copy. In deep copy, python will create an entirely separate list object that is not connected in source list in anyway, so when you make changes in one of them, the other is not affected. In shallow copy, the new list consists of pointers to the old list. So when you make changes in new list, the old list also changes. We will look at both ways to copy lists in python.

1. How to Shallow Copy List in Python

You can shallow copy using the default copy() function available for each list. We will copy the list and then change one element in our old list to see what happens to the new list.

>>> a = [[1, 2, 3], [4, 5, 6]]
>>> a
[[1, 2, 3], [4, 5, 6]]
>>> b=list(a)
>>> b
[[1, 2, 3], [4, 5, 6]]
>>> a[0][1] = 11
>>> a
[[1, 11, 3], [4, 5, 6]]
>>> b  
[[1, 11, 3], [4, 5, 6]]

In this case, when we change the old list after making a copy, it changes the new list also.

2. How to Deep Copy List in Python

You can deep copy list using deepcopy function. Here also we will copy the list and then change one element in our old list to see what happens to the new list.

>>> a = [[1, 2, 3], [4, 5, 6]]
>>> a
[[1, 2, 3], [4, 5, 6]]
>>> import copy
>>> a=[1,2,3]
>>> b=copy.deepcopy(a)
>>> b
[[1, 2, 3], [4, 5, 6]]
>>> a[0][1] = 11
>>> a
[[1, 11, 3], [4, 5, 6]]
>>> b
[[1, 2, 3], [4, 5, 6]]

In this case, when you we change the old list, the new list does not change.

In this article, we have learnt how to copy lists in python.

How to Copy List in Python