python - if a property sample work -

in book of "core python programming", there sample how use property. code this:

class hidex(object):     def __init__(self, x):         self.__x = x     @property     def x():         def fget(self):             return ~self.__x         def fset(self, x):             assert isinstance(val, int), 'val must int'             self.__x = ~x         return locals() 

the book says, class work following code:

inst = hidex(20) print inst.x inst.x = 30 print inst.x 

but don't think class work. because when access inst.x, interpreter run hidex.__dict__['x'].__get__(x, hidex), , because x = property(x), first arg 'fget' of property x, rather function 'fget' defined in x().

also, when run code, got result of:

{'fget': <function fset @ 0x.....>, 'self': <__main__.xxxx>, 'fget': <function fget @ 0x....>} traceback: ...... # result telling t.x = 30 cannot run, skip details attributeerror: cannot set attribute 

do miss something? why book intend can work?

this make sence:

class hidex(object):      def __init__(self, x):         self.__x = x      @property     def x(self):             return ~self.__x      @x.setter     def x(self, x):         assert isinstance(x, int), 'val must int'         self.__x = ~x 

looks @property in code of question not builtin different version.

this intended here:

def nested_property(func):     """make defining properties simpler.     """     names = func()     names['doc'] = func.__doc__     return property(**names)   class hidex(object):     def __init__(self, x):         self.__x = x     @nested_property     def x():         def fget(self):             return ~self.__x         def fset(self, x):             assert isinstance(x, int), 'val must int'             self.__x = ~x         return locals()