account.py

from functools import total_ordering


@total_ordering
class Account:
    'A simple account class'

    def __init__(self, owner, amount=0):
        'This is the constructor that lets us create objects from this class'
        self.owner = owner
        self.amount = amount
        self._transactions = []

    def __repr__(self):
        return 'Account({!r}, {!r})'.format(self.owner, self.amount)

    def __str__(self):
        return 'Account of {} with starting amount: {}'.format(self.owner,
                                                               self.amount)

    def add_transaction(self, amount):
        if not isinstance(amount, int):
            raise ValueError('please use int for amount')
        self._transactions.append(amount)

    @property
    def balance(self):
        return self.amount + sum(self._transactions)

    def __len__(self):
        return len(self._transactions)

    def __getitem__(self, position):
        return self._transactions[position]

    def __reversed__(self):
        return self[::-1]

    def __eq__(self, other):
        return self.balance == other.balance

    def __lt__(self, other):
        return self.balance < other.balance

    def __add__(self, other):
        owner = '{}&{}'.format(self.owner, other.owner)
        start_amount = self.amount + other.amount
        acc = Account(owner, start_amount)
        for t in list(self) + list(other):
            acc.add_transaction(t)
        return acc

    def __call__(self):
        print('Start amount: {}'.format(self.amount))
        print('Transactions: ')
        for transaction in self:
            print(transaction)
        print('\nBalance: {}'.format(self.balance))

    def __enter__(self):
        print('ENTER WITH: making backup of transactions for rollback')
        self._copy_transactions = list(self._transactions)
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        print('EXIT WITH:', end=' ')
        if exc_type:
            self._transactions = self._copy_transactions
            print('rolling back to previous transactions')
            print('transaction resulted in {} ({})'.format(exc_type.__name__, exc_val))  # noqa E501
        else:
            print('transaction ok')


if __name__ == '__main__':
    acc = Account('bob', 10)
    acc.add_transaction(20)
    acc.add_transaction(-10)
    acc.add_transaction(50)
    acc.add_transaction(-20)
    acc.add_transaction(30)
    assert acc.balance == 80
    assert list(reversed(acc)) == [30, -20, 50, -10, 20]