Python, copy list, list comprehension, slicing, copy(), deepcopy(), examples

How to Copy a List in Python (5 Techniques w/ Examples)

Python gives us multiple ways to copy a list. Depending on the method you choose, it can be as simple as a single line of code or as complicated as several lines of code. In this tutorial, we will explore five different techniques for copying lists in Python.

Technique 1: Using the list() Constructor

The most basic way to copy a list is by using the built-in list() constructor. You simply pass it the list that you want to copy as an argument and it will return a new list containing the elements from the original list. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list using the list() constructor
copied_list = list(my_list)

# Print the copied list
print(copied_list)
# Output: [1, 2, 3, 4]

With the list() constructor, you can also initialize an empty list and add the elements of the original list one by one. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list by creating an empty list and adding the elements
copied_list = []
for i in my_list:
    copied_list.append(i)

# Print the copied list
print(copied_list)
# Output: [1, 2, 3, 4]

Technique 2: Using the slice Operator [:]

Another simple way to copy a list is by using the slice operator [:]. To do this, you just specify the start and end indices with the slice operator, and the list will be copied automatically. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list using the slice operator
copied_list = my_list[:]

# Print the copied list
print(copied_list)
# Output: [1, 2, 3, 4]

Technique 3: Using the copy() Method

In Python, most lists have a copy() method that you can use to create a shallow copy of the list. This method is similar to the list() constructor but it is more efficient. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list using the copy() method
copied_list = my_list.copy()

# Print the copied list 
print(copied_list)
# Output: [1, 2, 3, 4]

Technique 4: Using the list() + extend() Methods

You can also combine the list() constructor and the extend() method to copy a list. This technique works by first creating a new empty list with the list() constructor and then concatenating the elements from the original list with the extend() method. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list using the list() + extend() methods
copied_list = list()
copied_list.extend(my_list)

# Print the copied list
print(copied_list)
# Output: [1, 2, 3, 4]

Technique 5: Using the loop + append() Method

Finally, you can use a loop and the append() method to copy a list. This technique works by creating an empty list and then iterating over the elements in the original list and appending them one by one to the new list. Here's an example:

# Initialize a list
my_list = [1, 2, 3, 4]

# Copy the list using the loop + append() method
copied_list = []
for i in my_list:
    copied_list.append(i)

# Print the copied list
print(copied_list)
# Output: [1, 2, 3, 4]

These are the five ways to copy a list in Python. As you can see, there are a few different techniques to choose from, so it's important to choose the right one for your use case.