Exception Handling

Errors and exceptions are common in programming. Python provides a robust way to handle them so your program doesn't crash unexpectedly. Instead of breaking, you can manage errors and continue running the program smoothly.

What are Errors and Exceptions?

1. Error: An issue in the code that prevents the program from running. For example:
• Syntax Errors (e.g., missing a colon : or parenthesis).
• Indentation Errors (e.g., improper spacing).
2. Exception: An error that occurs during the execution of a program. Examples:
• Division by zero.
• Accessing a variable that doesn't exist.

Example:

# This will raise a ZeroDivisionError
num = 10 / 0

Handling Exceptions with try and except

Python uses try and except blocks to handle exceptions. If an error occurs in the try block, the except block runs instead of crashing the program.

Basic Syntax:

try:
    # Code that may raise an exception
    risky_code()
except ExceptionType:
    # Code to handle the exception
    handle_error()

Example:

try:
    num = 10 / 0  # This will raise a ZeroDivisionError
except ZeroDivisionError:
    print("Cannot divide by zero!")

Multiple except Blocks

You can handle different types of exceptions with multiple except blocks.

Example:

try:
    num = int("hello")  # This will raise a ValueError
except ZeroDivisionError:
    print("Cannot divide by zero!")
except ValueError:
    print("Invalid input!")

Catching All Exceptions

You can use except without specifying an exception type to catch any error.

Example:

try:
    result = 10 / 0
except:
    print("An error occurred!")

Using else with try

The else block runs if there is no exception in the try block.

Example:

try:
    num = 10 / 2
except ZeroDivisionError:
    print("Cannot divide by zero!")
else:
    print("Division successful:", num)

The finally Block

The finally block always executes, whether there is an exception or not. Use it for cleanup tasks like closing files or releasing resources.

Example:

try:
    file = open("example.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found!")
finally:
    print("Closing the file...")
    if 'file' in locals() and not file.closed:
        file.close()

Raising Exceptions

You can raise exceptions intentionally using the raise keyword.

Example:

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

Custom Exceptions

You can create your own exception classes by inheriting from the built-in Exception class.

Example:

class CustomError(Exception):
    pass

try:
    raise CustomError("This is a custom error!")
except CustomError as e:
    print(e)

Common Exceptions in Python

Example Program

try:
    num = int(input("Enter a number: "))
    result = 10 / num
except ZeroDivisionError:
    print("You cannot divide by zero!")
except ValueError:
    print("Invalid input! Please enter a number.")
else:
    print("Division successful:", result)
finally:
    print("Execution completed.")

Output 1:

Output 2: