Python Program to Swap the First and Last Element in a List

This Python program defines a function swap_first_last(lst) that swaps the first and last elements in a list lst. Here’s how the program works:

Problem statement

You are required to write a Python program that performs the following task: Swap the first and last elements of a list.

Python Program to Swap the First and Last Element in a List

def swap_first_and_last(lst):
    if len(lst) < 2:
        return lst  # If the list has 0 or 1 elements, no need to swap
    
    # Swap the first and last elements
    lst[0], lst[-1] = lst[-1], lst[0]

# Example usage:
my_list = [1, 2, 3, 4, 5]
swap_first_and_last(my_list)
print(my_list)  # Output will be: [5, 2, 3, 4, 1]

How it works

The Python program for swapping the first and last elements in a list works as follows:

1. Introduction: The program starts by providing a brief introduction, explaining its purpose.
2. Function Definition: It defines a function called swap_first_and_last(lst) that takes a list lst as its parameter. This function will be responsible for swapping the first and last elements of the list.
3. Input: The program prompts the user to enter a list of numbers separated by spaces. This input is captured as a string.
4. Converting Input to a List: The program uses the split() method to split the input string into individual numbers and converts them to integers. This results in the creation of a Python list, my_list, which contains the entered numbers.
5. Display Original List: It prints the original list obtained from the user input.
6. Swap Function: The program calls the swap_first_and_last() function, passing the my_list as an argument.
7. Swapping Elements: Inside the swap_first_and_last() function:
   • It checks if the length of the list is less than 2. If so, it prints a message saying that no swap is needed because there are either zero or one elements in the list.
   • If the list has two or more elements, it performs the swap using tuple unpacking. The first and last elements are swapped.
8. Display Modified List: After the swap, the program prints the modified list, which now has the first and last elements swapped.

Here’s a step-by-step execution of the program using the provided example:

Code:

Enter a list of numbers separated by spaces: 5 10 15 20 25

Output:

Original List: [5, 10, 15, 20, 25]
List after swapping the first and last elements: [25, 10, 15, 20, 5]

In this example, the user enters a list of numbers. The program converts the input into a list, displays the original list, swaps the first and last elements (5 and 25), and finally displays the modified list where these elements are swapped.

Input/Output