Python: How to Access Elements in a List

In Python, there are two main ways to access elements in a list. The first approach is to use indices, and the second one is to use list slicing. Let’s explore them one by one in this practical, example-based article.

Accessing elements by index

Using positive index

Lists in Python are zero-based index. That means the first element of a list has an index of 0, the second element has an index of 1, and so on.

Using indexing allows you direct access to an individual element by its index position, as shown below:

# Creating a list
my_list = [1, 2, 3, 4, 5]

# Accessing the element at index 2
element = my_list[2]  
print(element) 

Output:

3

Using negative index

You can access elements from the end of a list without knowing the exact length.

Example:

# Creating a list
my_list = ["Programming", "Python", "Sling Academy"]

# # Accesses the last element in the list
last_element = my_list[-1] 
print(last_element)

Output:

Sling Academy

List slicing

Slicing a list in Python helps you extract a portion of the list by specifying a range of indices. It provides a flexible way to access multiple elements at once.

To slice a list, use the colon (:) notation to define a range of indices for the slice. The slice notation follows the pattern [start:stop:step], where start is the starting index (inclusive), stop is the stopping index (exclusive), and step is the increment size (optional).

Basic example:

# Creating a list
my_list = ['one', 'two', 'three', 'four', 'five']

# Retrieves elements from index 1 (inclusive) to 4 (exclusive)
subset = my_list[1:4] 
print(subset)

Output:

['two', 'three', 'four']

In this example, the slice my_list[1:4] returns a new list containing elements from index 1 up to, but not including, index 4.

Remember that Python lists are zero-based index. That’s why the first element in the resulting list is two.

Another example:

# Creating a list
my_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

# Retrieves elements from index 1 to 9 with a step size of 2
subset = my_list[1:9:2] 
print(subset)

Output:

[1, 3, 5, 7]

In the code snippet above, the slice my_list[1:9:2] returns a new list containing elements from index 1 to 9 with a step size of 2, effectively selecting every second element within that range.