P4.6.1Modifying the BankAccount class
(a) Modify the base BankAccount class (Section 4.6.2 of the book) to verify that the account number passed to its __init__ constructor conforms to the Luhn algorithm described in Exercise P2.5.3.
(b) Modify the CurrentAccount class to implement a free overdraft. The limit should be set in the __init__ constructor; withdrawals should be allowed to within the limit.
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(a) The definition of BankAccount in the code that follows uses the Luhn checksum method to validate the account number.
The account number may be provided as an integer or as a string (possibly with spaces or hyphens delimiting groups of numbers):
>>> from bank_account2 import BankAccount
>>> BankAccount('John Brown', 7298-904')
<bank_account2.BankAccount at 0x103fc1350>
>>> BankAccount('John Brown', 7298905)
...
ValueError: Invalid account number
(b) An interest-free overdraft is implemented in the CurrentAccount class below as well; a change has been made to the base class's BankAccount method to output negative balances cleanly.
>>> from bank_account2 import CurrentAccount
>>> account = CurrentAccount('John Brown', '729-8904', 0, 500)
>>> account.deposit(400)
>>> account.withdraw(350)
>>> account.check_balance()
The balance of account number 729-8904 is $50.00
>>> account.withdraw(200)
>>> account.check_balance()
The balance of account number 729-8904 is -$150.00
>>> account.withdraw(600)
$600.00 exceeds the single transaction limit of $500.00
>>> account.withdraw(500)
>>> account.check_balance()
The balance of account number 729-8904 is -$650.00
>>> account.withdraw(500)
Insufficient funds
The modified code is:
class BankAccount:
"""A abstract base class representing a bank account."""
currency = "$"
def __init__(self, customer, account_number, balance=0):
"""
Initialize the BankAccount class with a customer, account number
and opening balance (which defaults to 0.)
"""
self.customer = customer
self.set_account_number(account_number)
self.balance = balance
def set_account_number(self, account_number):
if not self.verify_account_number(account_number):
raise ValueError("Invalid account number")
self.account_number = account_number
def verify_account_number(self, account_number):
"""Verify the account number, returning True if it is valid."""
ccl = [int(d) for d in str(account_number) if d not in ("-", " ")]
for i in range(len(ccl) - 2, 0, -2):
ccl[i] *= 2
if ccl[i] > 9:
ccl[i] = 1 + (ccl[i] - 10)
checksum = sum(ccl) % 10
return not checksum
def deposit(self, amount):
"""Deposit amount into the bank account."""
if amount > 0:
self.balance += amount
else:
print("Invalid deposit amount:", amount)
def withdraw(self, amount):
"""
Withdraw amount from the bank account, ensuring there are sufficient
funds.
"""
if amount > 0:
if amount > self.balance:
print("Insufficient funds")
else:
self.balance -= amount
else:
print("Invalid withdrawal amount:", amount)
def check_balance(self):
"""Print a statement of the account balance."""
s_sign = "-" if self.balance < 0 else ""
print(
f"The balance of account number {self.account_number} is"
f" {s_sign}{self.currency}{abs(self.balance):.2f}"
)
class CurrentAccount(BankAccount):
"""A class representing a current (checking) account."""
def __init__(
self,
customer,
account_number,
annual_fee,
transaction_limit,
balance=0,
overdraft_limit=1000,
):
"""Initialize the current account."""
self.annual_fee = annual_fee
self.transaction_limit = transaction_limit
self.overdraft_limit = overdraft_limit
super().__init__(customer, account_number, balance)
def withdraw(self, amount):
"""
Withdraw amount if sufficient funds exist in the account and amount
is less than the single transaction limit.
"""
if amount <= 0:
print("Invalid withdrawal amount:", amount)
return
if amount > self.balance + self.overdraft_limit:
print("Insufficient funds")
return
if amount > self.transaction_limit:
print(
f"{self.currency}{amount:.2f} exceeds the single transaction"
f" limit of {self.currency}{self.transaction_limit:.2f}"
)
return
self.balance -= amount
def apply_annual_fee(self):
"""Deduct the annual fee from the account balance."""
self.balance = max(0.0, self.balance - self.annual_fee)