🟢 Beginner · Lesson 18

Exception Handling

What is Exception Handling?

Exception Handling means exception handling prevents a program from crashing when an error occurs during execution.

In real programs, this topic helps in handling wrong input. Learn the idea first, then type the program yourself and compare the output.

💡 At a Glance

Point	Details
Course Area	Core Python Basic programming concepts used to write Python programs.
Main Use	handling wrong input
Example File	`exception-handling.py`
Practice Focus	Run, change values, and explain the output line by line.

Why should you learn this?

It is useful for handling wrong input.
It connects with handling missing files.
It improves your ability to read, write and debug Python programs.

Important Terms

These terms are used directly in this lesson. Understand them before memorising the code.

Term	Meaning
try	Block where risky code is written.
except	Block that runs when a selected error occurs.
else	Runs when none of the previous conditions are true.
finally	Block that runs whether error occurs or not.
runtime error	Error that happens while the program is running.

Syntax / Basic Pattern

The simple pattern is: prepare data, apply the concept, then show the result.

Basic Pattern

try:
    number = int("abc")
    print(10 / number)
except ValueError:
    print("Invalid number format")
except ZeroDivisionError:
    print("Cannot divide by zero")
finally:

Complete Example Program

Python – exception-handling.py

try:
    number = int("abc")
    print(10 / number)
except ValueError:
    print("Invalid number format")
except ZeroDivisionError:
    print("Cannot divide by zero")
finally:
    print("Program completed")

Expected Output

Invalid number format Program completed

Program Explanation

try: is part of error handling.
number = int("abc") stores a value in number.
print(10 / number) displays information or calculated result on the screen.
except ValueError: is part of error handling.
print("Invalid number format") displays information or calculated result on the screen.
except ZeroDivisionError: is part of error handling.
print("Cannot divide by zero") displays information or calculated result on the screen.

Where will you use it?

Handling wrong input.
Handling missing files.
Preventing sudden program crash.

Common Mistakes

Writing code with wrong indentation.
Using input() value directly in calculations without converting it to int or float.
Using unclear variable names that make the program difficult to understand.

Practice Tasks

Type the program in exception-handling.py and run it.
Change input values or sample data and observe the new output.
Create one example related to handling wrong input.
Write 5 lines explaining the logic in your own words.

Summary

Exception Handling is not a theory-only topic. You should be able to explain the meaning, write the example, run it successfully, and use it in a small practical program.