Ron Adam wrote: > Erik Max Francis wrote: > >>Ron Adam wrote: >> >> >>>When you call a method of an instance, Python translates it to... >>> >>> leader.set_name(leader, "John") >> >> >>It actually translates it to >> >> Person.set_name(leader, "John") >> > > > I thought that I might have missed something there. > > Is there a paper on how python accesses and stores instance data and > methods? I googled but couldn't find anything that addressed this > particular question. > > >>> class a(object): > ... def x(self): > ... print 'x' > ... > >>> b = a() > >>> b > <__main__.a object at 0x009D1890> > >>> b.x > <bound method a.x of <__main__.a object at 0x009D1890>> > > So what exactly is a bound method object? Does it possibly translates > to something like the following? > > def x(*args, **kwds): > self = ? > return __class__.self(self, *args, **kwds) > > Cheers, > Ron > > > > >
All is explained at: http://users.rcn.com/python/download/Descriptor.htm#functions-and-methods and further at: http://www.python.org/pycon/2005/papers/36/pyc05_bla_dp.pdf "For objects, the machinery is in object.__getattribute__ which transforms b.x into type(b).__dict__['x'].__get__(b, type(b))." What follows is my interpretation - hope it's correct: # what exactly is a bound method object? # Illustrate b.f => type(b).__dict__['x'].__get__(b, type(b)) >>> class B(object): ... def f(self, x): ... return x or 42 ... >>> b = B() >>> type(b).__dict__['f'] <function f at 0x015052B0> # a plain old function >>> _.__get__(b, type(b)) # invoke the descriptor protocol # to make a bound method <bound method B.f of <Untitled7.B object at 0x01843D70>> >>> You don't have to use object.__getattribute__ to get a bound method. Nor does the function have to be in the class dictionary. You can just call any function descriptor yourself: >>> def g(self, y): ... return self.f(y) ... >>> boundg = g.__get__(b) # bind to B instance >>> boundg <bound method ?.g of <Untitled7.B object at 0x01843D70>> >>> boundg(0) 42 >>> Looked at this way, function.__get__ just does partial function application (aka currying). >>> def f(x, y): ... return x+y ... >>> add42 = f.__get__(42) >>> add42 <bound method ?.f of 42> >>> add42(1) 43 Michael -- http://mail.python.org/mailman/listinfo/python-list
