Handling IndexError Exception in Python list operation program

Last update on April 21 2025 13:08:31 (UTC/GMT +8 hours)

6. Handle IndexError in List Operations

Write a Python program that executes an operation on a list and handles an IndexError exception if the index is out of range.

exception IndexError:

Raised when a sequence subscript is out of range. (Slice indices are silently truncated to fall in the allowed range; if an index is not an integer, TypeError is raised.)

Sample Solution:

Code:

# Define a function named test_index that takes 'data' and 'index' as parameters.
def test_index(data, index):
    try:
        # Try to access an element at the specified 'index' in the 'data' list and store it in the 'result' variable.
        result = data[index]
        # Perform desired operation using the result (in this case, printing it).
        print("Result:", result)
    except IndexError:
        # Handle the exception if the specified 'index' is out of range for the 'data' list.
        print("Error: Index out of range.")

# Define a list of numbers 'nums'.
nums = [1, 2, 3, 4, 5, 6, 7]
# Prompt the user to input an index and store it in the 'index' variable.
index = int(input("Input the index: "))
# Call the test_index function with the 'nums' list and the user-provided 'index'.
test_index(nums, index)

Explanation:

In the above exercise,

The "perform_operation()" function takes two parameters: data, which represents the list, and index, which represents the index of the element.
Inside the function, we use a try block to access the element at the specified index in the list. If the index is within the list range, the element is assigned to the result variable.
We can then execute the desired operation using the result. In this example, we simply print the result.
If the index is out of range and an IndexError exception occurs, the program jumps to the except block.
In the except block, we catch the IndexError exception and print an error message indicating that the index is out of range.

Output:

Input the index: 0
Result: 1

Input the index: 4
Result: 5

Input the index: 9
Error: Index out of range.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program that attempts to access an element beyond the list length and catches the IndexError to print a custom message.
Write a Python program to implement a function that safely retrieves an element from a list given an index, returning a default value if out of range.
Write a Python program to iterate over a list using a for-loop and handle IndexError when accessing a specific index in a try-except block.
Write a Python program to demonstrate IndexError by intentionally accessing an invalid index and then using a fallback mechanism to avoid crashing.

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