What is a Negative Indexing in Python?

Negative indexing in Python allows you to access elements from the end of a sequence (string, list, tuple) by using negative numbers. Instead of counting from the beginning (0, 1, 2...), negative indexing counts backwards from the last element (-1, -2, -3...).

Understanding Negative Index Positions

In a string like "Python", the negative indices work as follows ?

Slicing Syntax with Negative Indexing

# Basic slicing syntax
sequence[start:stop:step]

# Examples with negative indexing
sequence[-4:-1]    # From 4th last to 2nd last
sequence[-5:]      # From 5th last to end
sequence[:-2]      # From beginning to 3rd last
sequence[::-1]     # Reverse entire sequence

Accessing Single Elements

You can access individual elements using negative indices ?

text = "Python"

print("Last character:", text[-1])
print("Second last character:", text[-2]) 
print("Third last character:", text[-3])

Last character: n
Second last character: o
Third last character: h

Slicing with Negative Indices

Extract substrings using negative start and stop positions ?

message = "Hello World!"

print("Original string:", message)
print("Last 6 characters:", message[-6:])
print("From -8 to -3:", message[-8:-3])
print("Every 2nd char from end:", message[::-2])

Original string: Hello World!
Last 6 characters: World!
From -8 to -3: o Wor
Every 2nd char from end: !lroW olleH

Reversing Strings

Use [::-1] to reverse any sequence completely ?

original = "Programming"

reversed_string = original[::-1]
print("Original:", original)
print("Reversed:", reversed_string)

Original: Programming
Reversed: gnimmargorP

Negative Indexing with Lists

Negative indexing works with all Python sequences, not just strings ?

numbers = [10, 20, 30, 40, 50]

print("List:", numbers)
print("Last element:", numbers[-1])
print("Last 3 elements:", numbers[-3:])
print("Reversed list:", numbers[::-1])

List: [10, 20, 30, 40, 50]
Last element: 50
Last 3 elements: [30, 40, 50]
Reversed list: [50, 40, 30, 20, 10]

Common Use Cases

Conclusion

Negative indexing in Python provides an intuitive way to access elements from the end of sequences. Use -1 for the last element, [-n:] for the last n elements, and [::-1] to reverse any sequence completely.