# newstyle.py

# extend builtin type
# from Guido's descrintro.html

class defaultdict(dict):
    def __init__(self, default=None):
        dict.__init__(self)
        self.default = default

    def __getitem__(self, key):
        try:
            return dict.__getitem__(self, key)
        except KeyError:
            return self.default

d = defaultdict('Oops!')
d[1] = 'abc'
print d[1]
print d[2]

print


# properties

class BankAccount(object):
    def __init__(self, initial_deposit=0.0):
        self.balance = initial_deposit

    def getbalance(self):
        print "Calling getbalance()"
        return self.__balance

    def setbalance(self, value):
        print "Calling setbalance() with", value
        if value < 0:
            raise ValueError, "Can't have negative balance"
        else:
            self.__balance = float(value)

    balance = property(getbalance, setbalance)

my_account = BankAccount(10000)
try:
    my_account.balance = -1
except ValueError, error:
    print error
print my_account.balance

print


# __slots__

class C(object):
    __slots__ = ['a', 'b']

x = C()
x.a = 1
print "x.a:", x.a
try:
    x.c = 2
except AttributeError:
    print "Can't set attributes not in __slots__"