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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-
try:
x = int(input(“Enter number: “))
print(10 / x)
except ZeroDivisionError:
print(“Zero is not allowed”)
else:
print(“Execution successful”)
-
- raise block
- This block is used to raise custom or predefined exceptions.
- For example –
- raise block
age = int(input(“Enter your age: “))
if age < 18:
raise ValueError(“Age must be 18 or above”)
-
- finally block
-
This block is used to execute whether an exception occurs or not.
-
It is used for cleanup operations.
- For example –
-
- finally block
try:
file1 = open(“data.txt”, “r”)
print(file1.read())
except FileNotFoundError:
print(“File not found”)
finally:
file1.close()
print(“Closing the file”)
-
- User-Defined (Custom) Exceptions
- This exception type is used to create our own or customized exception class.
- For example –
- User-Defined (Custom) Exceptions
class MyException(Exception):
pass
try:
num = int(input(“Enter a number: “))
if num < 0:
raise MyException(“Negative number not allowed”)
exceptMyException as e:
print(e)
Here, MyException is a user-defined class name, and it may also be any name, and Exception is a built-in base class.
Syntax
try:
# codes that may cause exceptions
except ExceptionType:
# code to handle exception
NB: We can also catch all exceptions (but it’s not recommended for large programs) using an except block without specifying an exception type. e.g.-
try:
x = int(“Welcome”)
except:
print(“An error occurred”)
Example
try:
a = int(input(“Enter a number: “))
b = 10 / a
print(b)
except ZeroDivisionError:
print(“Division by zero is not allowed”)
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
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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") 
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