Subclasses and Constructor Inheritance in Python

Notes on subclasses and constructor inheritance in Python.

__metaclass__ = type

class A():
  
  def __init__(self):
    self.foo = True
  
  def bar(self):
    if self.foo:
      print 'Foo is TRUE!'
    else:
      print 'Foo is NOT true.'

a = A()
a.bar() # Prints "Foo is TRUE!"


class B(A):

  'Subclass of A without inherited constructor.'
  
  def __init__(self):
    self.color = 'Red'
    
  def printColor(self):
    print self.color
    
b = B()
b.printColor() # Prints "Red"
#b.bar() # Throws and error because self.foo doesn't exist in class B!


class C(A):
  
  'Subclass of A with constructor inherited the older way.'

  def __init__(self):
    self.fruit = 'Banana!'
    #A.__init__(self) # This is the old way of inheriting a superclass constructor.
    super(C, self).__init__() # This is the new way of inheriting a superclass constructor. 
                              # Note that super() needs to get the superclass of C().
  def printFruit(self):
    print self.fruit
 
 
c = C()
c.printFruit() # Prints "Banana!"
c.bar() # Prints "Foo is TRUE!"