Exception handling Concept in Python:-

Exception handling Concept in Python:-

Exception means unexpected run time error, which will be occurred during the execution of the program.

It is used to handle unexpected run time errors of the program to solve another program code interruption.

A project is a set of programs, if one program will be interrupted then the complete project will be destroyed hence we should always implement exception handling to protect program interruption in an application.

Python provides a try-except block to manage the exception block in the python program.

try block is used to represent code and except block will be used to write error message.

Exception handling is mandatory in all program codes hence we should always exception handling under python script.

Some Exceptions can be raised by hardware issues, software issues, network issues, permission issues, disk failures.

Basic Syntax of Exception on Python:-

1)   Only Try and Except:-

try:

   CODE BLOCK

   CODE BLOCK

except :

    ErrorMessage

2)   Try--Except with Classname

try:

   CODE BLOCK

   CODE BLOCK

except ExceptionClassname :

    ErrorMessage

3)   TRY with Multiple Except Block

try:

   CODE BLOCK

   CODE BLOCK

except ExceptionClass1 :

    ErrorMessage

except ExceptionClass2 :

    ErrorMessage

4)  TRY ---- EXCEPT ------ FINALLY

try:

   CODE BLOCK

   CODE BLOCK

except ExceptionClass1 :

    ErrorMessage

finally:

    Default block

5)   TRY ----  EXCEPT  ---- ELSE and Finally:-

try:

   CODE BLOCK

   CODE BLOCK

except ExceptionClass1 :

    ErrorMessage

else:

   Statements

finally:

    Default block

6)  TRY...... EXCEPT ---- ELSE:-

try:

   CODE BLOCK

   CODE BLOCK

except ExceptionClass1 :

    ErrorMessage

else:

    Default block

Example of Exception Handling:-

try:

  a=  int(input("enter first number"))

  b = int(input("enter second number"))

  c=a/b

  print(c)

except ZeroDivisionError ex:

  print ('denominator can not be zero")

How to Handle Multiple Exception in Program:-

try:

  a=  int(input("enter first number"))

  b = int(input("enter second number"))

  c=a/b

  print(c)

except ZeroDivisionError:

  print ('denominator can not be zero')

except ValueError:

  print ('enter only numeric value')  

print("Line1")

print("Line2")

...................................................................................................................................................

.....................................................................................................................................................

finally:-

It will be executed with exception and without exception means it is the default block that will be executed whenever an exception will be occurred or not.

try:

   statements

except Exception:

     Error Message

finally:

    Default Statement

It is used to provide acknowledgment or dispose of object data.

try:

  a=  int(input("enter first number"))

  b = int(input("enter second number"))

  c=a/b

  print(c)

except ZeroDivisionError:

  print ('denominator can not be zero')

except ValueError:

  print ('enter only numeric value')  

finally:

  print('finally')

   print("Line1")

print("Line2")

..................................................................

else:-  It is the opposite of except, if the exception will not occur and we want to do something then we can write code on the else block. It is the opposite of except block.

try:

  statements

  statements

except ExceptionClassname

  statements

  statements

else:

  statements

Example of Try..except--else --finally

try:

  a=  int(input("enter first number"))

  b = int(input("enter second number"))

  c=a/b

  print(c)

except ZeroDivisionError:

  print ('denominator can not be zero')

except ValueError:

  print ('enter only numeric value')

else:

  print("NOT ANY ERROR")  

finally:

  print('finally')

  

print("Line1")

print("Line2")

Note:- Exception is the base class for all type of Exceptions

try:

  a=  int(input("enter first number"))
  b = int(input("enter second number"))
  c=a/b
  print(c)
except Exception:
  print ('error')

else:
  print("NOT ANY ERROR")
finally:
  print('finally')
print("Line1")
print("Line2")

Complete Program of Exception Which Contain Try--except.

flag=True
count=0
while(flag):
 try:
  a = int(input("enter first number"))
  b = int(input("enter second number"))
  c=a/b
  print(c)
 except ValueError:
  print("enter only numeric")
 except ZeroDivisionError:
  print("denominator can not be zero")
 else:
  flag=False
 finally:
  count=count+1
  print("Number of attempt "+str(count))

Complete Example of Exception:-

c=0

s=''

try:

 a= int(input("enter first number"))

 b= int(input("enter second number"))

 c=a/b

 except ZeroDivisionError:

    s = 'Result is default'

    print("denominator can not be zero")

except ValueError:

    s='Result is default'

    print("Enter only numeric value")

else:

    s="Result is Accurate "

finally:

    print(s,c)

Sr.No.	Exception Name & Description
1	Exception Base class for all exceptions
2	StopIteration Raised when the next() method of an iterator does not point to any object.
3	SystemExit Raised by the sys. exit() function.
4	StandardError Base class for all built-in exceptions except StopIteration and SystemExit.
5	ArithmeticError Base class for all errors that occur for numeric calculation.
6	OverflowError Raised when a calculation exceeds maximum limit for a numeric type.
7	FloatingPointError Raised when a floating-point calculation fails.
8	ZeroDivisionError Raised when a division or modulo by zero takes place for all numeric types.
9	AssertionError Raised in case of failure of the Assert statement.
10	AttributeError Raised in case of failure of attribute reference or assignment.
11	EOFError Raised when there is no input from either the raw_input() or input() function and the end of file is reached.
12	ImportError Raised when an import statement fails.
13	KeyboardInterrupt Raised when the user interrupts program execution, usually by pressing Ctrl+c.
14	LookupError Base class for all lookup errors.
15	IndexError Raised when an index is not found in a sequence.
16	KeyError Raised when the specified key is not found in the dictionary.
17	NameError Raised when an identifier is not found in the local or global namespace.
18	UnboundLocalError Raised when trying to access a local variable in a function or method but no value has been assigned to it.
19	EnvironmentError Base class for all exceptions that occur outside the Python environment.
20	IOError Raised when an input/ output operation fails, such as the print statement or the open() function when trying to open a file that does not exist.
21	IOError Raised for operating system-related errors.
22	SyntaxError Raised when there is an error in Python syntax.
23	IndentationError Raised when indentation is not specified properly.
24	SystemError Raised when the interpreter finds an internal problem, but when this error is encountered the Python interpreter does not exit.
25	SystemExit Raised when Python interpreter is quit by using the sys.exit() function. If not handled in the code, causes the interpreter to exit.
26	TypeError Raised when an operation or function is attempted that is invalid for the specified data type.
27	ValueError Raised when the built-in function for a data type has the valid type of arguments, but the arguments have invalid values specified.
28	RuntimeError Raised when a generated error does not fall into any category.
29	NotImplementedError Raised when an abstract method that needs to be implemented in an inherited class is not actually implemented.

User define exception in Python:-

We can create our own exception classes to manage the exception-based program, Python uses class and object concepts to implement user-defined Exceptions.

Now I am creating Salary Exception where if the Salary will be less than` 10000 then it will raise an exception otherwise display a salary.

Syntax of User define an exception

class  Classname(Exception):

       pass

Example of exception:-

class SalaryException(Exception):

    pass

try:

 sal = int(input("Enter salary of employee"))

 if sal<10000:

    raise SalaryException

 else:

     print("Salary is "+str(sal))

    

except SalaryException:

    print("Salary should be above 10000")

What is the raise?

raise is a keyword that is used to call Exception, it is similar to the Java throw keyword.

ASSIGNMENTS of Exception handling:-

1)  Manage mark sheet program with all possible exception

2)  WAP to validate mobile number using the Exception?

3)  Create a program for addition, subtraction, multiplication, and division using multiple exception block.

4)  Create user-defined exceptions when student fees are>500000 otherwise display fees?

5)  Define 10 predefine exceptions with possible examples?