They just need some pointers on how the new language

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They just need some pointers on how the new language can help them achieve these goals. Advanced Topics Types and Objects object is the built-in object that serves as the ancestor of all new-style classes. type is an object of type 'type' that serves as the ancestor of all built-in types and metaclasses. If you find triple entendre in a programming language more annoying that amusing, just remember this diagram: object --> type --> metaClassX | | --> inheritance right --> \ - --> - --> ClassX | | instantiation down objX Exercise Write the simplest possible program with a metaclass, a class, and an instance of that class. Use the functions type(), issubclass(), isinstance(), to explore the relationships among these objects. >>> object <type 'object'> >>> type <type 'type'> >>> issubclass(type,object) True >>> class metaClassX(type): pass >>> class ClassX(object): __metaclass__ = metaClassX >>> objX = ClassX() >>> isinstance(objX,ClassX) True >>> isinstance(objX,metaClassX) False >>> isinstance(ClassX,metaClassX) True >>> isinstance(ClassX,object) True >>> issubclass(ClassX,object) True >>> issubclass(metaClassX,type) True
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>>> issubclass(metaClassX,object) True >>> issubclass(ClassX,type) False >>> type(ClassX) <class '__main__.metaClassX'> >>> type(metaClassX) <type 'type'> >>> dir(object) ['__class__', '__delattr__', '__doc__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__'] >>> dir(type) ['__base__', '__bases__', '__basicsize__', '__call__', '__class__', '__cmp__', '__delattr__', '__dict__', '__dictoffset__', '__doc__', '__flags__', '__getattribute__', '__hash__', '__init__', '__itemsize__', '__module__', '__mro__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__subclasses__', '__weakrefoffset__', 'mro'] >>> ClassX <class '__main__.ClassX'> >>> dir(ClassX) ['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__', '__hash__', '__init__', '__metaclass__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__'] >>> dir(objX) ['__class__', '__delattr__', '__dict__', '__doc__', '__getattribute__', '__hash__', '__init__', '__metaclass__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', '__weakref__'] >>> ClassX.__dict__ <dictproxy object at 0x008FD590> >>> ClassX.__dict__.keys() ['__dict__', '__weakref__', '__module__', '__metaclass__', '__doc__'] >>> object.__dict__.keys() ['__setattr__', '__reduce_ex__', '__new__', '__reduce__', '__str__', '__getattribute__', '__class__', '__delattr__', '__repr__', '__hash__', '__doc__', '__init__'] >>> ### class metametaClassX(type): mm1 = 'mm1' def __init__(cls,name,bases,cdict): cls.mm1 = metametaClassX.mm1 class metaClassX(type): __metaclass__ = metametaClassX m1 = 'm1' def __init__(cls,name,bases,cdict): cls.m1 = metaClassX.m1 cls.mm1 = metaClassX.mm1 class ClassX(object):
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__metaclass__ = metaClassX c1 = 'c1' objX = ClassX() for x in objX,ClassX,metaClassX,metametaClassX: print type(x) ###
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Christopher Reinemann
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