class Number:  
  def __init__(self, start):  
    self.data = start  
  def __sub__(self, other): #minus method  
    return Number(self.data - other)  
number = Number(20)  
y = number – 10 # invoke __sub__ method 
class Number: 
  def __init__(self, start): 
    self.data = start 
  def __sub__(self, other): #minus method 
    return Number(self.data - other) 
number = Number(20) 
y = number – 10 # invoke __sub__ method

class indexer:  
  def __getitem__(self, index): #iter override  
    return index ** 2 
X = indexer()  
X[2]  
for i in range(5):  
  print X[i] 
class indexer: 
  def __getitem__(self, index): #iter override 
    return index ** 2 
X = indexer() 
X[2] 
for i in range(5): 
  print X[i]

class stepper:  
  def __getitem__(self, i):  
    return self.data[i]  
X = stepper()  
X.data = 'Spam' 
X[1] #call __getitem__  
for item in X: #call __getitem__  
  print item 
class stepper: 
  def __getitem__(self, i): 
    return self.data[i] 
X = stepper() 
X.data = 'Spam' 
X[1] #call __getitem__ 
for item in X: #call __getitem__ 
   print item

class empty:  
  def __getattr__(self,attrname):  
    if attrname == 'age':  
      return 40 
    else:  
      raise AttributeError,attrname  
X = empty()  
print X.age #call__getattr__  
class accesscontrol:  
  def __setattr__(self, attr, value):  
    if attr == 'age':  
      # Self.attrname = value loops!  
      self.__dict__[attr] = value  
    else:  
      print attr  
      raise AttributeError, attr + 'not allowed' 
X = accesscontrol()  
X.age = 40   #call __setattr__  
X.name = 'wang' #raise exception 
class empty: 
  def __getattr__(self,attrname): 
    if attrname == 'age': 
      return 40 
    else: 
      raise AttributeError,attrname 
X = empty() 
print X.age #call__getattr__ 
class accesscontrol: 
  def __setattr__(self, attr, value): 
    if attr == 'age': 
      # Self.attrname = value loops! 
      self.__dict__[attr] = value 
    else: 
      print attr 
      raise AttributeError, attr + 'not allowed' 
X = accesscontrol() 
X.age = 40   #call __setattr__ 
X.name = 'wang' #raise exception

class adder:  
  def __init__(self, value=0):  
    self.data = value  
  def __add__(self, other):  
    self.data += other  
class addrepr(adder):  
  def __repr__(self):  
    return 'addrepr(%s)' % self.data  
x = addrepr(2) #run __init__  
x + 1    #run __add__  
print x   #run __repr__ 
class adder: 
  def __init__(self, value=0): 
    self.data = value 
  def __add__(self, other): 
    self.data += other 
class addrepr(adder): 
  def __repr__(self): 
    return 'addrepr(%s)' % self.data 
x = addrepr(2) #run __init__ 
x + 1    #run __add__ 
print x   #run __repr__

class Prod:  
  def __init__(self, value):  
    self.value = value  
  def __call__(self, other):  
    return self.value * other  
p = Prod(2) #call __init__  
print p(1) #call __call__  
print p(2) 
class Prod: 
  def __init__(self, value): 
    self.value = value 
  def __call__(self, other): 
    return self.value * other 
p = Prod(2) #call __init__ 
print p(1) #call __call__ 
print p(2)

class Life:  
  def __init__(self, name='name'):  
    print 'Hello', name  
    self.name = name  
  def __del__(self):  
    print 'Goodby', self.name  
brain = Life('Brain') #call __init__  
brain = 'loretta'  # call __del__