Python

Python List -1 Index

Python is defined as a zero-indexed language because all calculations begin at zero it is also left and right exclusive when specifying a numeric range. This is true for objects such as lists as well as Series, where the first element has an index of 0. We must supply both the beginning index and the ending index when generating ranges or slicing a range of values from a list-like object.

This is when the language of left inclusive and right exclusive comes into play. The left index is to be added in the returned range or slice. With examples, we’ll go through the Python list -1 index in this post.

What is Python List Index?

A list is a container that stores objects of various data kinds in an ordered sequence (ints, floats, strings, Boolean, and so on). It’s a crucial data structure that Python is built on. The data is enclosed in square brackets ([]), with commas between the values (,).

The list’s items are indexed from zero to one, with the first entry starting at index 0. You can edit the produced list by adding new items, altering existing ones, or deleting them. Duplicate entries and a nested list are also possible.

On a list, there are numerous methods available, one of which is the index ().

The index() function in Python returns the index of the element passed on. This method receives an argument and returns the index of that parameter. It throws a ValueError if the element isn’t there. If a list contains duplicate elements, the index of the first occurring element is returned. This method accepts two additional optional parameters, start, and end, which are used to limit the index search.

Use of Negative Indexing in the List

In most computer languages, indexing starts at 0 for arrays and lists.

However, Python has a unique feature called negative indexing. Negative indexing is basically the process of indexing a list from the outset with indexing starting at -1, i.e., -1 provides the list’s last element, -2 provides the list’s second last item, and so on.

The process of Negative indexing can be used to u or even display data from the end of a list. Additionally, it can also be used to reverse a number or even text without the need for extra steps.

Example 1:

The ‘len’ and ‘index’ methods are used to acquire the negative index of an element in a list when it is required. A demonstration of this concept can be found below. A list of integers is defined in the code and presented on the screen.

On the screen, a key is defined and displayed. The difference between the list’s length and the element present at a given key is calculated. This is a variable that has been allocated to it. This is seen in the following screenshots provided below.

Try to understand the following code. We’ve made an array with the values 43, 56, 32, 76, 33, 22, and 11 in it. The list was then printed with the key value supplied. Following that, we create a variable which we call the len() and val.index functions. The array and key value were also given as arguments. Finally, the result of the function’s execution is shown on the screen.

list_val = [43, 56, 32, 76, 33, 22, 11]
print("The list is as follows:")
print(list_val)
key_val = 32
print("The key value is as follows:")
print(key_val)
outcome = len(list_val) - list_val.index(key_val)
print("The output is as follows:")
print(outcome)

This is the output, which includes the list, key value, and result.

Example 2:

Indexes are employed in arrays in all computer languages, as we all know. The indexes of an array’s elements can be traversed to access the items available in an array. However, no computer language allows us to specify a negative index value like -4.

Negative indexing can be done in Python, which is not accessible in other programming languages. This means that -1 represents the array’s final element, whereas -2 represents the array’s second final element. The array’s negative indexing starts at the end. This indicates that the final element of the array is -1, which is the first negative indexing element.

The code below, which explains how to create an array as you can see in the starting line. The array has values of 11, 24, 45, 87, 44, and 88. Following that, we attempted to retrieve the elements at positions -1 and -2, as seen below.

arr = [11,24, 45, 87, 44, 88]
print (arr[-1])
print (arr[-2])

The numbers (88 and 44) at the -1 and -2 positions of the array are shown below.

Example 3:

We will insert the element in the -1 index of an array in this example. We have built an array named ‘list_val’ in the first line of code. The array contains four elements. These elements are ‘Apple,’ ‘Orange,’ ‘Banana,’ and ‘Grapes’ as you can see. The original array was then printed, and the insert() method was used to add the specified element to the -1 index of the array. Finally, the array is updated and presented.

list_val = ['Apple', 'Orange', 'Banana', 'Grapes']
print('Original Array:', list_val)
list_val.insert(-1, 'Apple Juice')
print('Array after inserting element at -1 index:', list_val)

Here’s the output which includes both the original and the new array to which the desired element has been added. See below.

Conclusion:

This article goes over the Python list index() function in great detail. Our major goal was to obtain an element using the -1 index. In addition, we’ve included instructions for adding an element to the array at the -1 index. All of these ideas are well explained with examples for your guidance. Refer to these guidelines for a clear idea of the Python list -1 index.

About the author

Kalsoom Bibi

Hello, I am a freelance writer and usually write for Linux and other technology related content