Introduction to Exceptions in Python

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Introduction to Exceptions in Python

An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions.

In Python: Errors are represented as exception objects If an exception occurs and is not handled, the program terminates with an error message Python provides a powerful way to handle exceptions using try, except blocks

Why Handle Exceptions?

Common Exceptions in Python

Example 1: Unhandled Exception

a = 5 / 0

ZeroDivisionError: division by zero

Explanation: Division by zero causes an exception and the program stops execution.

Example 2: Basic Exception Handling

try:
    result = 10 / 0
except ZeroDivisionError:
    print("You cannot divide by zero!")

You cannot divide by zero!

Explanation: The program does not crash — the exception is handled.

Example 3: Handling Multiple Exceptions

try:
    num = int("abc")
except ValueError:
    print("Invalid conversion!")
except ZeroDivisionError:
    print("Division by zero!")

Invalid conversion!

Example 4: Catching All Exceptions (Not Recommended)

try:
    x = undefined_variable
except Exception as e:
    print("Error occurred:", e)

Error occurred: name 'undefined_variable' is not defined

How Exception Handling Works

try:
    # Code that may raise an exception
except ExceptionType:
    # Code that runs if exception occurs
else:
    # Code that runs if no exception occurs
finally:
    # Code that always runs (cleanup)

Key Points

Exceptions are runtime errors that can disrupt the program try…except block is used to handle exceptions Multiple exceptions can be handled finally block always runs — used for cleanup (e.g., closing files)

Summary

• Exceptions help manage error-prone situations gracefully
• Without handling, exceptions terminate the program
• Use try…except…finally for robust error handling
• Common exceptions: ZeroDivisionError, ValueError, IndexError, etc.

Next, we will cover Try, Except, Else, Finally in more detail — and see how you can structure robust error-handling logic in Python.