class BankAccount:
    """ Class definition modeling the behavior of a simple bank account """

    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        …
    def deposit(self, amount):
        """Deposits the amount into the account."""
        …
    def withdraw(self, amount):
        """
        Withdraws the amount from the account.  Each withdrawal resulting in a
        negative balance also deducts a penalty fee of 5 dollars from the balance.
        """
        …
    def get_balance(self):
        """Returns the current balance in the account."""
        …
    def get_fees(self):
        """Returns the total fees ever deducted from the account."""
        …

The deposit and withdraw methods each change the account balance. The withdraw method also deducts a fee of 5 dollars from the balance if the withdrawal (before any fees) results in a negative balance. Since we also have the method get_fees, you will need to have a variable to keep track of the fees paid.

Here's one possible test of the class. It should print the values 10 and 5, respectively, since the withdrawal incurs a fee of 5 dollars.

my_account = BankAccount(10)
my_account.withdraw(15)
my_account.deposit(20)
print my_account.get_balance(), my_account.get_fees()