Exception Handling in Python

Introduction

• Exception handling is an OOPs concept of Python.

Definition

• An exception is an error that occurs during program execution or run time.

Characteristics

• Exception handling in Python is a mechanism used to handle runtime errors (exceptions) so that the normal flow of a program is not interrupted. Instead of crashing, the program can respond gracefully by handling an exception.

Advantages or Need of Exception Handling

• It prevents abnormal program crashes or termination.
• It improves program reliability.
• It separates error-handling code from normal code.
• It helps in debugging and maintenance.
• It improves program robustness.
• It helps in error recovery.
• It makes code cleaner and more readable.

Elements of Exception Handling

• Exception handling in Python uses try, except, else, finally, and raise keywords to manage runtime errors effectively, ensuring smooth program execution.
• The following major elements are used to catch and handle exceptions that arise suddenly.
  • try block
  • except block
  • else block
    • This block is used mainly when no exception occurs. eg- 

• • raise block
    • This block is used to raise custom or predefined exceptions.
    • For example –

• • finally block
    • This block is used to execute whether an exception occurs or not.
    • It is used for cleanup operations. 
    • For example –

Example

Built-in Exceptions in Python

Some common Built-in Exceptions of Python are –

          Exception Type Name     –     Description

• ZeroDivisionError   –    Division by zero
• ValueError  –    Invalid value
• TypeError   –    Wrong data type
• IndexError  –    Index out of range
• KeyError    –     Dictionary key missing
• FileNotFoundError   –    File not found

=======================  XXX  ========================

Program Examples on Exception Handling

Example : A Python program to handle multiple exceptions.

try:
    x = int(input("Enter First Number: "))
    y = int(input("Enter Second Number: "))
    print(x / y)
except ZeroDivisionError:
    print("Cannot divide by zero")
except ValueError:
    print("Invalid input! Enter integers only")

Example : A Python program to handle Invalid Input Exceptions.

try:
    num = int(input("Enter an integer: "))
    print("You entered:", num)
except ValueError:
    print("Error: Invalid input, enter integers only")

Output:
Enter an integer: hhh
Error: Invalid input, enter integers only

Example : A Python program to handle Specific Exceptions.

try:
    f = open("sample.txt", "r")
    print(f.read())
except FileNotFoundError:
    print("Error: File does not exist")

--------------  OR  --------------

try:
    arr = [10, 20, 30]
    print(arr[5])
except IndexError:
    print("Index out of range")

--------------  OR  --------------

try:
    d = {"name": "Ravi", "age": 20}
    print(d["marks"])
    #print(d["age"])
except KeyError:
    print("Key not found in dictionary")

--------------  OR  --------------

try:
    result = "10" + 5
except TypeError:
    print("Type mismatch error")

Example : A Python program to handle All/General Exceptions.

try:
    x = int("abc")
except Exception as e:
    print("Error:", e)

Output:
Error: invalid literal for int() with base 10: 'abc'

--------------  OR  --------------

try:
    x = int("10.23")
except Exception as e:
    print("Error:", e)

Output:
Error: invalid literal for int() with base 10: '10.23'

--------------  OR  --------------

try:
    x = (10.23+"abc")
except Exception as e:
    print("Error:", e)

Output:
Error: unsupported operand type(s) for +: 'float' and 'str'