Exception Handling in Python

A system to trap the runtime error when the program is in execution.

Use try and except keywords to trap some runtime error

Python provides a built-in class Exception to trap the error message

Use raise keyword to send some error message using the Exception class

Example 1
def factorial(n):
    if(n<0):
        raise Exception("Sorry! Number must be >=0")
    f=1
    i=1
    while i<=n:
        f=f*i
        i=i+1
    return f

try:
    n=int(input("Enter a number : "))
    print("Factorial of",n,"is",factorial(n))
except Exception as e:
    print("Error : ",e)


Example 2: Custom Exception
class InvalidNumberException(Exception):
    def __init__(self,message):
        self.message=message
    def __str__(self):
        return self.message

def factorial(n):
    if(n<0):
        raise InvalidNumberException("Sorry! Number must be >=0")
    f=1
    i=1
    while i<=n:
        f=f*i
        i=i+1
    return f

try:
    n=int(input("Enter a number : "))
    print("Factorial of",n,"is",factorial(n))
except InvalidNumberException as e:
    print("Error : ",e)
except ValueError as e:
    print("Please provide some number")


Example 3
class Customer:
    def __init__(self,cid,name,opamount):
        if(opamount)<1:
            raise Exception("Sorry! Invalid Amount to open the account")
        self.cid=cid
        self.name=name
        self.balance=opamount
    def setName(self,name):
        self.name=name
    def getCid(self):
        if not self.cid.isdigit():
            raise Exception("Invalid Customer ID")
        return self.cid
    def getName(self):
        return self.name
    def getBalance(self):
        return self.balance
    def deposit(self,amount):
        if(amount<1):
            raise Exception("Sorry! Invalid amount to deposit")
        self.balance=self.balance+amount
    def withdraw(self,amount):
        if(amount>self.balance):
            raise Exception("Sorry! Insufficient balance")
        self.balance=self.balance-amount

try:
    cid=int(input('Customer ID'))
    name=input('Customer Name')
    balance=float(input('Opening Amount'))
    c=Customer(cid,name,balance)
    amount=float(input('Add amount'))
    c.deposit(amount)
    amount=float(input('Withdarw amount'))
    c.withdraw(amount)
    print("Balance of",c.getName(),"is",c.getBalance())
except ValueError as e:
    print("Invalid customer id")
except Exception as e:

    print("Error ",e)


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