Python exception Handling

1. 🧩 What is Exception Handling?
• An exception is an error that occurs while your code
is running — for example, dividing by zero or trying
to open a file that doesn’t exist.
• Instead of letting your program crash, exception
handling lets you catch and handle those errors
gracefully.

2. 🧱 Basic Syntax
• try:
• # code that may cause an error
• except:
• # code that runs if an error occurs

3. 🧠 Example 1 — Basic
Try/Except
• try:
• num = int(input('Enter a number: '))
• result = 10 / num
• print('Result:', result)
• except:
• print('Something went wrong!')
• If the user enters 0 → ZeroDivisionError
• If the user enters a letter → ValueError
• The except block catches both and prevents crashing.

4. 🧱 Example 2 — Handling
Specific Exceptions
• try:
• num = int(input('Enter a number: '))
• result = 10 / num
• print('Result:', result)
• except ValueError:
• print('❌ Please enter a valid number.')
• except ZeroDivisionError:
• print('❌ Cannot divide by zero.')

5. 🧱 Example 3 — Using else and finally
• try:
• num = int(input('Enter a number: '))
• result = 10 / num
• except ZeroDivisionError:
• print('Division by zero is not allowed.')
• else:
• print('Result is:', result)
• finally:
• print('Program execution complete.')
• else → runs if no exception occurs
• finally → always runs (cleanup code)

6. Real time Example - Finally
•Closing files
•Releasing resources
•Disconnecting from databases
•Ending network connections

7. 🧱 Example 4 — Raising Your
Own Exception
• age = int(input('Enter your age: '))
• if age < 0:
• raise ValueError('Age cannot be negative.')
• print('Your age is:', age)

8. 🧱 Example 5 — Custom
Exception Class (Advanced)
• class InvalidAgeError(Exception): //user-defined exception class
• pass
• try:
• age = int(input('Enter age: '))
• if age < 0:
• raise InvalidAgeError('Age cannot be negative.')
• except InvalidAgeError as e:
• print('Custom Error:', e)

9. ✅
Summary
Keyword Purpose
try Code that might
throw an error
except Handles the error
else Runs if no error
occurs
finally Always runs
(cleanup code)
raise Manually raise an
exception