Using Python

8.20 DevelopaclassBankAccountthatsupportsthesemethods:

__init__(): Initializes the bank account balance to the value of the input argument, or to 0 if no input argument is given

withdraw(): Takes an amount as input and withdraws it from the balance

deposit(): Takes an amount as input and adds it to the balance

balance(): Returns the balance on the account

 >>> x = BankAccount(700) >>> x.balance() 700.00 >>> x.withdraw(70) 

 >>> x.balance() 630.00 >>> x.deposit(7) >>> x.balance() 637.00 

8.40 InProblem8.20,therearesomeproblemswiththeimplementationoftheclassBankAccount, and they are illustrated here:

 >>> x = BankAccount(-700) >>> x.balance() -700 >>> x.withdraw(70) 

 >>> x.balance() -770 >>> x.deposit(-7) >>> x.balance() Balance: -777 

The problems are: (1) a bank account with a negative balance can be created, (2) the with- drawal amount is greater than the balance, and (3) the deposit amount is negative. Modify the code for the BankAccount class so that a ValueError exception is thrown for any of these violations, together with an appropriate message: 'Illegal balance', 'Overdraft', or 'Negative deposit'.

 >>> x = BankAccount2(-700) Traceback (most recent call last): ... ValueError: Illegal balance 

8.41 InProblem8.40, a generic Value Error exception is raised if any of the three violations occur. It would be more useful if a more specific, user-defined exception is raised instead. Define new exception classes NegativeBalanceError, OverdraftError, and DepositError that would be raised instead. In addition, the informal string representa- tion of the exception object should contain the balance that would result from the negative balance account creation, the overdraft, or the negative deposit.

For example, when trying to create a bank account with a negative balance, the error message should include the balance that would result if the bank account creation was al- lowed:

>>> x = BankAccount3(-5)

Traceback (most recent call last):

...

NegativeBalanceError: Account created with negative balance -5

When a withdrawal results in a negative balance, the error message should also include the balance that would result if the withdrawal was allowed:

>>> x = BankAccount3(5)

>>> x.withdraw(7)

Traceback (most recent call last):

...

OverdraftError: Operation would result in negative balance -2

If a negative deposit is attempted, the negative deposit amount should be included in the error message:

>>> x.deposit(-3)

Traceback (most recent call last):

...

DepositError: Negative deposit -3

Finally, reimplement the class BankAccount to use these new exception classes instead of ValueError.