Python Class

class A(object): def __init__(self): self.x = 'Hello' def method_a(self, foo): print self.x + ' ' + foo

... the self variable represents the instance of the object itself. Most object-oriented languages pass this as a hidden parameter to the methods defined on an object; Python does not. You have to declare it explicitly. When you create an instance of the A class and call its methods, it will be passed automatically, as in ...

a = A() # We do not pass any argument to the __init__ method a.method_a('Sailor!') # We only pass a single argument

The __init__ method is roughly what represents a constructor in Python. When you call A() Python creates an object for you, and passes it as the first parameter to the __init__ method. Any additional parameters (e.g., A(24, 'Hello')) will also get passed as arguments--in this case causing an exception to be raised, since the constructor isn't expecting them.