Understanding the Python Data Model

# http://docs.python.org/reference/datamodel.html

class Demo(object):
    # This method gets called on every access to self.something
    # It is implemented in "object", the base class for every
    # python object, and looks roughly like this:
    def __getattribute__(self, name):
        # Debug print
        print("__getattribute__('%s')" % name)
        # Look for instance attribute
        d = object.__getattribute__(self, "__dict__")
        if d.has_key(name):
            return d[name]
        # Look for class attribute
        cls = object.__getattribute__(self, "__class__")
        d = cls.__dict__
        if d.has_key(name):
            a = d[name]
            # Wrap unbound methods
            if callable(a):
                def bound_method(*argv, **argn):
                    return a(self, *argv, **argn)
                return bound_method
            else:
                return a
        raise AttributeError("'%s' object has no attribute '%s'" % (cls.__name__, name))

    x = 1 # A class attribute

    def __init__(self):
        self.y = 2 # An instance attribute

    def method(self, z): # A method
        return self.x + self.y + z

# Try in a console:
o = Demo()
o.x
o.y
o.hello = "world"
o.hello
Demo.this_is = "a test"
o.this_is
o.method
o.method(3)

# Remove the __getattribute__ implementation and re-run the tests
# above to see that it does work the same way.