⭐ Exception Handling in Python

Exception Handling is a mechanism used to detect and manage errors during program execution.
Instead of crashing the program when an error occurs, Python provides a safe way to handle it and continue execution.

⭐ What Is Exception Handling? (Exam Definition)

Exception handling is the process of responding to runtime errors (exceptions) in a controlled manner using try, except, else, finally, and raise statements.

It prevents the program from terminating unexpectedly.

⭐ Why Do We Need Exception Handling?

✔ Prevent program crashes
✔ Handle errors gracefully
✔ Provide meaningful error messages
✔ Improve user experience
✔ Allow program to continue execution
✔ Debugging becomes easier

⭐ Basic Exception Handling Structure

Python uses the following syntax:

try:
    # Code that may cause an exception
except:
    # Code to handle the exception

⭐ Example 1: Basic try-except

try:
    x = 10 / 0
except:
    print("Error: Cannot divide by zero")

Output:

Error: Cannot divide by zero

⭐ Multiple Except Blocks

Used to handle specific exceptions:

try:
    a = int("abc")
except ValueError:
    print("Value Error occurred")
except TypeError:
    print("Type Error occurred")

⭐ Catching Multiple Exceptions in One Line

try:
    x = 10 + "Hello"
except (TypeError, ValueError):
    print("Some error occurred")

⭐ Using Exception Object

try:
    x = 10 / 0
except Exception as e:
    print("Exception:", e)

⭐ The `else` Block

The else block executes only when no exception occurs.

try:
    x = int("123")
except ValueError:
    print("Invalid input")
else:
    print("Conversion successful:", x)

⭐ The `finally` Block

The finally block always executes, whether an exception occurs or not.
Useful for cleanup tasks: closing files, releasing resources, etc.

try:
    f = open("myfile.txt")
    data = f.read()
except FileNotFoundError:
    print("File does not exist")
finally:
    print("Execution completed!")

⭐ try-except-else-finally (Full Structure)

try:
    # risky code
except:
    # handle error
else:
    # runs when no error
finally:
    # always runs

⭐ Raising Exceptions (raise)

Used to throw an exception manually.

age = -5
if age < 0:
    raise ValueError("Age cannot be negative")

⭐ User-Defined Exceptions

You can create your own exceptions using classes.

class MyError(Exception):
    pass

try:
    raise MyError("Something went wrong!")
except MyError as e:
    print(e)

⭐ Practical Example: Handling Multiple Errors

try:
    a = int(input("Enter number: "))
    b = int(input("Enter another: "))
    print(a / b)
except ValueError:
    print("Invalid number")
except ZeroDivisionError:
    print("You cannot divide by zero!")
except Exception as e:
    print("Unknown error:", e)
finally:
    print("Program finished")

⭐ Flow of Exception Handling

Code inside try executes
If an exception occurs → Python jumps to matching except block
If no exception occurs → else executes
finally executes in all cases

⭐ Advantages of Exception Handling

✔ Prevents abnormal termination
✔ Improves reliability
✔ Separates error-handling logic from normal logic
✔ Makes programs robust and maintainable

⭐ Exam-Ready Summary

Exceptions are runtime errors that stop program execution
Python handles them using try, except, else, finally, raise
try: code that may cause error
except: handles error
else: runs if no error occurs
finally: always runs
Custom exceptions can be created using classes

Exception handling