Exception Handling

 

Exception Handling in Python

1. Built-in Exceptions

Python provides many predefined exceptions that occur during program execution when an error happens.

Common built-in exceptions include:

Exception	Description
ZeroDivisionError	Occurs when dividing by zero
TypeError	Occurs when wrong data type is used
ValueError	Occurs when invalid value is given
IndexError	Occurs when index is out of range
KeyError	Occurs when dictionary key is not found
FileNotFoundError	Occurs when file does not exist

Example:

a = 10
b = 0
print(a / b)

Output:

ZeroDivisionError: division by zero

2. Handling Exceptions

Exceptions can be handled using try and except blocks.

Syntax

try:
    # code that may cause error
except ExceptionType:
    # handling code

Example

try:
    a = int(input("Enter a number: "))
    b = int(input("Enter another number: "))
    print(a / b)
except ZeroDivisionError:
    print("Cannot divide by zero")

3. Exception with Arguments

Exceptions can pass arguments or messages to provide more details about the error.

Example

try:
    x = int("hello")
except ValueError as e:
    print("Error occurred:", e)

Output:

Error occurred: invalid literal for int()

Here e stores the exception message.

4. Raising Exceptions

Sometimes programmers intentionally generate exceptions using the raise keyword.

Syntax

raise ExceptionType("Error Message")

Example

age = int(input("Enter age: "))

if age < 18:
    raise ValueError("Age must be 18 or above")
else:
    print("Eligible")

5. User-Defined Exceptions

Programmers can create custom exceptions by creating a class derived from Exception.

Example

class InvalidMarks(Exception):
    pass

marks = int(input("Enter marks: "))

try:
    if marks > 100:
        raise InvalidMarks
    print("Marks accepted")
except InvalidMarks:
    print("Marks cannot be greater than 100")

6. Assertions in Python

Assertions are used for debugging purposes to check whether a condition is true.

If the condition is false, Python raises an AssertionError.

Syntax

assert condition, "Error message"

Example

x = int(input("Enter a number: "))

assert x >= 0, "Number must be positive"

print("Number is:", x)

If a negative number is entered, the output will be:

AssertionError: Number must be positive