59.1.1. Exception - An overview
(a) Exception is an event which occurs to disrupt the flow of the given program.
(b) Exception handling is a rich feature provided by Python language.
(d) If the code executes without any error, the except block is skipped and control goes to the statement after the except block.
59.1.2. Types of Exceptions and base exceptions
(a) All exceptions should be instances of the derived class of the BaseException class.
(b) In the except block, if the exception is handled, it means it can also handle all the exception types that are derived from this Exception class.
(d) All built-in exceptions are derived from the Exception class.
59.1.3. A simple try except example
num1 = int(input("num1: "))
num2 = int(input("num2: "))
try:
# implement try block here
print(num1 / num2)
except:
# implement except block here
print("exception occurred")
59.1.4. Built-in Exceptions list.
(a) The root exception class is the BaseException.
(b) SystemExit, KeyboardInterrupt, GeneratorExit and Exception extend from the BaseException.
(c) The Rest of the built-in classes are derived from The Exception class.
59.1.5. Simple try except block example
try:
num1 = int(input("num1: "))
num2 = int(input("num2: "))
# perform division operator
print(num1/num2)
except ZeroDivisionError:
# print respective error
print("Error: Division by zero is not allowed")
except ValueError:
# print respective error
print("Error: Invalid input. Please enter valid integers")
59.1.6. Nested Try blocks and Exceptions
TryAgain = True
while TryAgain:
try:
Value = int(input("whole number: "))
except ValueError:
print("you must enter a whole number!")
try: # Nested try block
# Prompt to try again and handle responses here
inp = input("try again (y/n)? ")
if inp == "y" or inp == "Y":
TryAgain = True
else:
TryAgain = False
except: # Nested exception block
print("ok, see you next time!")
TryAgain = False
# Check user's response and update TryAgain here
except KeyboardInterrupt:
# Handle keyboard interrupt here
TryAgain = False
else:
print(Value)
TryAgain = True
