Index and Slice Lists in Python

Lists are one of the four most commonly used data structures provided by Python. A list is a data structure in python that is mutable and has an ordered sequence of elements. Following is a list of integer values.

lis= [1,2,3,4,5]
print(lis)

If you execute the above snippet, produces the following output.

[1, 2, 3, 4, 5]

In this article, we will discuss how to index and slice lists in python.

Indexing Lists

In Python, every list with elements has a position or index. Each element of the list can be accessed or manipulated by using the index number.

They are two types of indexing ?

• Positive Indexing
• Negative Indexing

Positive Indexing

In positive the first element of the list is at an index of 0 and the following elements are at +1 and as follows.

In the below figure, we can see how an element is associated with its index or position.

Example

The following is an example code to show positive indexing of lists.

list= [5,2,9,7,5,8,1,4,3]
print(list[2])
print(list[5])

Output

The above code produces the following results

9
8

Negative Indexing

In negative indexing, the indexing of elements starts from the end of the list. That is the last element of the list is said to be at a position at -1 and the previous element at -2 and goes on till the first element.

In the below figure, we can see how an element is associated with its index or position.

Example

The following is an example code to show the negative indexing of lists.

list= [5,2,9,7,5,8,1,4,3]
print(list[-2])
print(list[-8])

Output

The above code produces the following results

4
2

Slicing List

List slicing is a frequent practice in Python, and it is the most prevalent technique used by programmers to solve efficient problems. Consider a Python list. You must slice a list in order to access a range of elements in it. One method is to utilize the colon as a simple slicing operator (:).

The slice operator allows you to specify where to begin slicing, where to stop slicing, and what step to take. List slicing creates a new list from an old one.

Syntax

The syntax for list is as follows.

List[Start : Stop : Stride]

The above expression returns the portion of the list from index Start to index Stop, at a step size Stride.

Example

In the following example we have used the slice operation to slice a list. We also use negative indexing method to slice a list.

list= [5,2,9,7,5,8,1,4,3]
print(list[0:6])
print(list[1:9:2])
print(list[-1:-5:-2])

Output

The above code produces the following results

[5, 2, 9, 7, 5, 8]
[2, 7, 8, 4]
[3, 1]