We are going to train our OOP skill by implementing a few classes, which will represent a cash desk.

The cash desk will do the following things:

• Take money as single bills
• Take money as batches (пачки!)
• Keep a total count
• Tell us some information about the bills it has

Create a class, called Bill which takes one parameter to its constructor - the amount of the bill - an integer.

This class will only have dunders so you wont be afraid of them anymore!

The class should implement:

• __str__ and __repr__
• __int__
• __eq__ and __hash__
• If amount is negative number, raise an ValueError error.
• If type of amount isn't int, raise an TypeError error.

Here is an example usage:

from cashdesk import Bill

a = Bill(10)
b = Bill(5)
c = Bill(10)

int(a) # 10
str(a) # "A 10$ bill"
print(a) # A 10$ bill

a == b # False
a == c # True

money_holder = {}

money_holder[a] = 1 # We have one 10% bill

if c in money_holder:
    money_holder[c] += 1

print(money_holder) # { "A 10$ bill": 2 }

We are going to implement a class, which represents more than one bill. A BatchBill!

The class takes a list of Bills as the single constructor argument.

The class should have the following methods:

• __len__(self) - returns the number of Bills in the batch
• total(self) - returns the total amount of all Bills in the batch

We should be able to iterate the BatchBill class with a for-loop.

Here is an example:

from cashdesk import Bill, BillBatch

values = [10, 20, 50, 100]
bills = [Bill(value) for value in values]

batch = BillBatch(bills)

for bill in batch:
    print(bill)

# A 10$ bill
# A 20$ bill
# A 50$ bill
# A 100$ bill

In order to do that, you need to implement the following method:

def __getitem__(self, index):
    pass

Finally, implement a CashDesk class, which has the following methods:

• take_money(money), where money can be either Bill or BatchBill class
• total() - returns the total amount of money currenly in the desk
• inspect() - prints a table representation of the money - for each bill, how many copies of it we have.

For example:

from cashdesk import Bill, BillBatch, CashDesk

values = [10, 20, 50, 100, 100, 100]
bills = [Bill(value) for value in values]

batch = BillBatch(bills)

desk = CashDesk()

desk.take_money(batch)
desk.take_money(Bill(10))

print(desk.total()) # 390
desk.inspect()

# We have a total of 390$ in the desk
# We have the following count of bills, sorted in ascending order:
# 10$ bills - 2
# 20$ bills - 1
# 50$ bills - 1
# 100$ bills - 3