Python workshop part 2: Objects and list comprehension

README.txt

This code is not complete: One of the tests currently fails and the Transaction class is not used.  Can you fix it?

account.py

"""
Session 2:
Object oriented programming and Test Driven Development with Python

Dirk P. Janssen - Fall 2017


This code is working but not functionally complete:  The 'largewithdrawals'
method does not work, as is shown by one failing test.   You can use the
Transaction class that we already wrote, but there are other ways to solve
this.

Bonus points:  For each new method or attribute, try to think hard
where it fits best.  Which class has the most natural respoonsibility for this
method or attribute?

"""

class Account(object):
    """
    Simple bank account supporting withdrawal and deposit
    """

    def __init__(self):
        self.balance = 0

    def withdraw(self, amount):
        newbalance = self.balance - amount
        if newbalance >= 0:
            self.balance = newbalance
        else:
            raise ValueError("Cannot withdraw this much, balance is %f" % self.balance)

    def deposit(self, amount):
        self.balance += amount


class Transaction():
    """
    This class holds a single transaction
    IT IS CURRENTLY NOT USED
    """

    action = ""
    amount = 0

    def __init__(self, action, amount):
        self.action = action
        self.amount = amount

    def __str__(self):
        return "%s %.2f" % (self.action, self.amount)


class HistoryAccount(Account):

    def __init__(self):
        super().__init__()
        self.historyList = []

    def history(self):
        return self.historyList

    def deposit(self, amount):
        super().deposit(amount)
        self.historyList.append("deposit %.2f" % amount)

    def withdraw(self, amount):
        super().withdraw(amount)
        self.historyList.append("withdraw %.2f" % amount)

    def largewithdrawals(self):
        "return all withdrawals over 10 dollars"
        # this is called a list comprehension in python:
        return [ x for x in self.historyList if "withdraw" in x ]

test_account.py

"""
Test for account.py.

There are several ways to run tests in python, running 'nose2' from
the command line is one of the easiest methods.

"""

import unittest
from account import Account, HistoryAccount, Transaction

class AccountTest(unittest.TestCase):

    def test_withdrawal(self):
        a = Account()
        a.balance = 100
        a.withdraw(40)
        self.assertEqual(a.balance, 60)


class TransactionTest(unittest.TestCase):

    def test_str(self):
        t = Transaction("give", 12.3)
        self.assertEqual(str(t), "give 12.30")


class HistoryTest(unittest.TestCase):

    def test_hasBalance(self):
        a = HistoryAccount()

        self.assertEqual(a.balance, 0)


    def test_hasEmptyHistory(self):
        a = HistoryAccount()
        history = a.history()

        self.assertEqual(len(history), 0)


    def test_hasHistory(self):
        a = HistoryAccount()
        a.deposit(100)
        a.withdraw(40)
        history = a.history()

        self.assertEqual(len(history), 2)
        self.assertEqual("deposit 100.00", history[0])
        self.assertEqual("withdraw 40.00", history[1])


    def test_hasLargeWithdrawals(self):
        """"

        TODO

        this test does not work right now, it will return
        2 transactions (both withdrawals) but does not filter out
        the withdrawal of 4 dollars"""
        a = HistoryAccount()
        a.deposit(100)
        a.withdraw(40)
        a.withdraw(4)

        largewithdrawals = a.largewithdrawals()
        self.assertEqual(len(largewithdrawals), 1)
        self.assertEqual("withdraw 40.00", largewithdrawals[0])