# Multiple inheritance
class Account(object):
    """A bank account that allows deposits and withdrawals."""

    interest = 0.02

    def __init__(self, account_holder):
        self.balance = 0
        self.holder = account_holder

    def deposit(self, amount):
        """Increase the account balance by amount and return the new
        balance."""
        self.balance = self.balance + amount
        return self.balance

    def withdraw(self, amount):
        """Decrease the account balance by amount and return the new
        balance."""
        if amount > self.balance:
            return 'Insufficient funds'
        self.balance = self.balance - amount
        return self.balance

class CheckingAccount(Account):
    """A bank account that charges for withdrawals."""

    withdraw_fee = 1
    interest = 0.01

    def withdraw(self, amount):
        fee = self.withdraw_fee
        return Account.withdraw(self, amount+fee)

class SavingsAccount(Account):
    """A bank account that charges for deposits."""

    deposit_fee = 2

    def deposit(self, amount):
        return Account.deposit(self, amount - self.deposit_fee)

class AsSeenOnTVAccount(CheckingAccount, SavingsAccount):
    """A bank account that charges for everything."""

    def __init__(self, account_holder):
        self.holder = account_holder
        self.balance = 1           # A free dollar!

# Method resolution order
supers = [c.__name__ for c in AsSeenOnTVAccount.mro()]

# Error messages
from operator import add

def curry(f):
    def outer(x):
        def inner(*args):
            return f(x, *args)
        return inner
    return outer

add3 = curry(add)(3)
# add3(4, 5)

tom_account = Account('Tom')
# tom_account.deposit(100, 200)

# Inheritance and polymorphism
def welfare(account):
    """Deposit $100 into an account if it has less than $100."""
    if account.balance < 100:
        return account.deposit(100)

alice_account = CheckingAccount('Alice')
welfare(alice_account)
bob_account = SavingsAccount('Bob')
welfare(bob_account)

# String representations
import datetime
today = datetime.date(2012, 10, 8)
repr(today)
str(today)

# Special methods and properties
from fractions import gcd

class Rational(object):
    """A mutable fraction.

    >>> f = Rational(3, 5)
    >>> f
    Rational(3, 5)
    >>> print(f)
    3/5
    >>> f.float_value
    0.6
    >>> f.numerator = 4
    >>> f.float_value
    0.8
    >>> f.denominator -= 3
    >>> f.float_value
    2.0
    """

    def __init__(self, numer, denom):
        g = gcd(numer, denom)
        self.numerator = numer // g
        self.denominator = denom // g

    @property
    def float_value(self):
        return self.numerator / self.denominator

    def __repr__(self):
        return 'Rational({0}, {1})'.format(self.numerator,
                                           self.denominator)

    def __str__(self):
        return '{0}/{1}'.format(self.numerator, self.denominator)

    def __add__(self, num):
        denom = self.denominator * num.denominator
        numer1 = self.numerator * num.denominator
        numer2 = self.denominator * num.numerator
        return Rational(numer1 + numer2, denom)

    def __mul__(self, num):
        return Rational(self.numerator * num.numerator,
                        self.denominator * num.denominator)

    def __eq__(self, num):
        return (self.numerator == num.numerator and
                self.denominator == num.denominator)

    def __bool__(self):
        return self.numerator != 0