Module 2.13 : Exception Handling

Introduction

Errors are common in programming. When a program encounters an unexpected problem, it may stop executing and display an error message.

In Python, such runtime errors are called Exceptions.

If exceptions are not handled properly, programs may crash unexpectedly. Python provides a powerful mechanism called Exception Handling to manage errors gracefully.

Exception handling allows developers to detect, control, and respond to errors without terminating the program.

This concept is widely used in Artificial Intelligence, Data Science, Web Development, Automation, and Software Engineering.

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Learning Objectives

• Understand exceptions in Python.
• Learn the difference between errors and exceptions.
• Use try and except blocks.
• Understand else and finally blocks.
• Use raise statements.
• Create custom exceptions.
• Apply exception handling in real-world applications.

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What is an Exception in Python?

An exception is an event that interrupts the normal execution flow of a program.

Exceptions occur during runtime when Python encounters invalid operations.

Example:

print(10/0)

Output:

ZeroDivisionError:
division by zero

Here, Python generates an exception because division by zero is mathematically invalid.

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Why Exception Handling is Important

Exception handling is important because it prevents programs from crashing unexpectedly.

Without exception handling:

• Programs terminate immediately.
• User experience becomes poor.
• Data processing may fail.
• Applications become unstable.

Exception handling allows developers to:

• Catch errors.
• Display meaningful messages.
• Continue program execution.
• Improve software reliability.

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Common Types of Exceptions

Python provides many built-in exceptions.

Exception	Description
ZeroDivisionError	Division by zero
NameError	Undefined variable
TypeError	Invalid data type operation
ValueError	Invalid value supplied
IndexError	Invalid index access
FileNotFoundError	Missing file

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The try and except Block

Python uses try and except blocks to handle exceptions.

Syntax

try:
    risky code

except:
    error handling code

Example

try:
    print(10/0)

except:
    print("Cannot divide by zero")

Output:

Cannot divide by zero

Instead of crashing, the program handles the error safely.

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Handling Specific Exceptions

It is considered a good practice to handle specific exceptions.

Example

try:
    value = int("Python")

except ValueError:
    print("Invalid Number")

Output:

Invalid Number

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Handling Multiple Exceptions

A program can handle multiple exception types.

Example

try:
    number = int(input("Enter Number: "))
    result = 10/number

except ValueError:
    print("Invalid Input")

except ZeroDivisionError:
    print("Zero Not Allowed")

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The else Block

The else block executes only if no exception occurs.

Example

try:
    x = 10/2

except ZeroDivisionError:
    print("Error")

else:
    print("Success")

Output:

Success

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The finally Block

The finally block always executes whether an exception occurs or not.

It is commonly used for cleanup tasks such as closing files or database connections.

Example

try:
    print(10/2)

except:
    print("Error")

finally:
    print("Execution Completed")

Output:

5.0
Execution Completed

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The raise Statement

Python allows programmers to manually generate exceptions using the raise keyword.

Example

age = -5

if age < 0:
    raise ValueError("Age cannot be negative")

Output:

ValueError:
Age cannot be negative

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Custom Exceptions

Python allows developers to create their own exception classes.

Example

class InvalidSalary(Exception):
    pass

salary = -1000

if salary < 0:
    raise InvalidSalary("Salary cannot be negative")

Custom exceptions are useful for large applications and enterprise software.

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Exception Handling in Artificial Intelligence

Exception handling is extremely important in Artificial Intelligence and Data Science projects.

Common applications:

• Handling missing datasets.
• Managing invalid model inputs.
• Preventing prediction failures.
• Managing file loading errors.
• Handling API response failures.

AI systems must handle errors carefully because they often work with massive datasets and external resources.

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Real-World Examples

Login Validation Example

try:

    password = input("Enter Password: ")

    if len(password) < 6:
        raise ValueError("Password Too Short")

    print("Valid Password")

except ValueError as e:

    print(e)

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ATM Withdrawal Example

balance = 5000

try:

    withdraw = 7000

    if withdraw > balance:
        raise Exception("Insufficient Balance")

except Exception as e:

    print(e)

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Python Example

try:

    number = int(input("Enter Number: "))

    print(100/number)

except ZeroDivisionError:

    print("Cannot divide by zero")

except ValueError:

    print("Enter valid integer")

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Interview Questions

1. What is an exception in Python?

An exception is a runtime event that interrupts program execution.

2. Which keyword is used to handle exceptions?

The except keyword.

3. What is the purpose of finally?

The finally block executes regardless of whether an exception occurs.

4. What does the raise statement do?

It manually generates exceptions.

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Assignment

1. Create a division program using try-except.
2. Handle ZeroDivisionError.
3. Handle ValueError using user input.
4. Create a custom exception example.
5. Use finally in a file handling example.

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Quiz

Q1. Which keyword handles exceptions?

• A. try
• B. except
• C. break
• D. def

Answer: B. except

Q2. Which block always executes?

• A. else
• B. except
• C. finally
• D. try

Answer: C. finally

Q3. Which keyword manually creates exceptions?

• A. import
• B. return
• C. raise
• D. continue

Answer: C. raise

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Summary

In this tutorial, you learned Exception Handling in Python. You explored exceptions, try-except blocks, else, finally, raise statements, and custom exceptions.

Exception handling is essential for building reliable applications because it prevents crashes and improves program stability.

Understanding exception handling is important for Artificial Intelligence, Data Science, Automation, and Software Development.

Next Tutorial

Tutorial 19: Modules and Packages

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