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Python method resolution demo
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
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