Python Exception Handling

Exception Handling is the process of handling runtime errors in a program. It prevents the program from crashing and allows it to continue running smoothly.

An exception is an error that occurs during program execution.

Common Exceptions

Exception	Description
ZeroDivisionError	Division by zero
ValueError	Invalid value
TypeError	Invalid operation between data types
NameError	Variable not defined
IndexError	Invalid list index
KeyError	Dictionary key not found
FileNotFoundError	File does not exist

Handling ZeroDivisionError

Example

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

Output:

Cannot divide by zero

Handling ValueError

Example

try:
    age = int("abc")
except ValueError:
    print("Invalid value")

Output:

Invalid value

Handling TypeError

Example

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

Output:

Type mismatch

Handling NameError

Example

try:
    print(username)
except NameError:
    print("Variable not found")

Output:

Variable not found

Handling IndexError

Example

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

Output:

Index out of range

Handling KeyError

Example

try:
    student = {"name": "John"}
    print(student["age"])
except KeyError:
    print("Key not found")

Output:

Key not found

Handling FileNotFoundError

Example

try:
    file = open("data.txt")
except FileNotFoundError:
    print("File not found")

Output:

File not found

Handling Multiple Exceptions

Example

try:
    num = int(input("Enter a number: "))
    result = 10 / num

except ValueError:
    print("Invalid input")

except ZeroDivisionError:
    print("Cannot divide by zero")

Using Exception as a Variable

Example

try:
    print(10 / 0)

except Exception as error:
    print(error)

Output:

division by zero

Raising Exceptions

You can create exceptions manually using the raise keyword.

Example

age = -5

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

Output:

ValueError: Age cannot be negative

Custom Exceptions

Example

class InvalidAgeError(Exception):
    pass

age = -1

if age < 0:
    raise InvalidAgeError("Invalid Age")

Output:

InvalidAgeError: Invalid Age

Summary

• Exception handling manages runtime errors.
• Exceptions prevent programs from crashing unexpectedly.
• Different exception types handle different errors.
• Multiple exceptions can be handled separately.
• The raise keyword creates exceptions manually.
• Custom exceptions can be created by inheriting from Exception.
• Proper exception handling improves application reliability.