Python method resolution demo

method-demo.py

class Desc(object):
    def __init__(self, msg):
        self.msg = msg
    
    def __get__(self, instance, owner=None):
        return "{0}: {1}".format(self.typ, self.msg)

    
class NonDesc(Desc):
    # non-data descriptor 
    typ = 'NonDesc'


class DataDesc(Desc):
    # data descriptor
    typ = 'DataDesc'

    def __set__(self, instance, value):
        pass

    def __delete__(self, instance):
        pass


class M(type):
    x = 'x from M'
    y = NonDesc('y from cls M')
    z = DataDesc('z from cls M')
    
    def __getattr__(self, name):
        return "getattr M {0}".format(name)


class A(object):
    #t = 't from A'
    #u = NonDesc('u from cls A')
    #v = DataDesc('v from cls A')
    x = 'x from A'
    y = NonDesc('y from cls A')
    z = DataDesc('z from cls A')


class B(A):
    """
    metaclass is M
    """
    __metaclass__ = M
    
    
class C(B):
    """
    metaclass is inherited from C
    """
    def __getattr__(self, name):
        return "getattr C: {0}".format(name)
    

c = C()
print '******'
print 'c.__class__', c.__class__
print 'c.__class__.__getattribute__', c.__class__.__getattribute__
print 'c.__class__.__mro__', c.__class__.__mro__

print '******'
print 'c.x', c.x
print 'c.y', c.y
print 'c.z', c.z
print 'c.nope', c.nope

c.t = 't from obj c'
c.u = NonDesc('u from obj c')
c.v = DataDesc('v from obj c')
c.x = 'x from obj c'
c.y = NonDesc('y from obj c')
c.z = DataDesc('z from obj c')

print '******'
print 'c.t', c.t
print 'c.u', c.u
print 'c.v', c.v
print 'c.x', c.x
print 'c.y', c.y
print 'c.z', c.z


print '******'
print "C.x", C.x
print "C.y", C.y
print "C.z", C.z
print "C.nope", C.nope

C.t = 't from obj C'
C.u = NonDesc('u from obj C')
C.v = DataDesc('v from obj C')
C.x = 'x from obj C'
C.y = NonDesc('y from obj C')
C.z = DataDesc('z from obj C')

print '******'
print "C.t", C.t
print "C.u", C.u
print "C.v", C.v
print "C.x", C.x
print "C.y", C.y
print "C.z", C.z
print "C.nope", C.nope