exception ni python ppt

1. What is Exception?
• An exception is an event, which occurs during the execution of a program, that disrupts the normal
flow of the program's instructions.
• In general, when a Python script encounters a situation that it can't cope with, it raises an
exception. An exception is a Python object that represents an error.
• When a Python script raises an exception, it must either handle the exception immediately
otherwise it would terminate and come out.
Handling an exception:
If you have some suspicious code that may raise an exception, you can defend your program by placing
the suspicious code in a try: block. After the try: block, include an except: statement, followed by a block
of code which handles the problem as elegantly as possible.
Syntax:
try:
You do your operations here;
......................
except Exception I:
If there is ExceptionI, then execute this block.
except Exception II:
If there is ExceptionII, then execute this block.
......................
else:
If there is no exception then execute this block.

2. Example
try:
a=int(input("Enter value of a"))
b=int(input("Enter the value of b"))
c=a/b
print("Result=",c)
except Exception:
print("can't divide by zero")
else:
print("Hi i am else block")
Output
Enter value of a25
Enter the value of b5
Result= 5.0
Hi i am else block
Enter value of a10
Enter the value of b0
can't divide by zero
Contain code that may throw the exception
Execute code if there is some exception in try block
And exception name is optional
Run this code if no exception occurs

3. Declaring multiple exception
Python allow us to declare the multiple exceptions with the escept clause.
Syntax:
try:
#block of code
except(<Exception1>,<Exception2>,……<Exception n>)
#block of code
else:
#block of code
Example:
try:
a=10/0
except (ArithmeticError ,SystemError):
print("Arithmatic exception")
else:
print("Successfully done")
Output
Arithmatic exception

4. The finally block
we can use finally block with try block in which we place important code which must be executed
before try statement
throws an exception.
Syntax
try:
#block of code
#this may throw an exception
finally:
#block of code
#important code that will always executed

5. Example:
try:
fileptr=open("LICENSE.txt","r")
try:
fileptr.write("Hi i am good")
finally:
fileptr.close()
print("file closed")
except:
print("Error")
Output:
file closed
Error

6. Raising an Exception
An exce[ption can be raised by using the raise clause in python.