Hello Dieter,
Thanks for taking time to explain this. I understood it half way, but that is my problem. I need to spend some more months to feel in home I guess. As you saw from documentation link, those are just words kind of spec. Which source you recommend to read which explains these concepts more with example codes. Otherwise, I think the list will be flooded by questions from me as there are so many things I feel like abstract. I found Python official tutorial more explanatory and not much questions came while I was reading it. But it didn’t cover everything, it explains as a tutorial does. I am reading https://docs.python.org/3/reference/index.html now, and it seems like saying what Python can do, but not going deep to explain it to a new comers most of the time. Thanks, Arup Rakshit a...@zeit.io > On 20-Apr-2019, at 10:59 AM, dieter <die...@handshake.de> wrote: > > Arup Rakshit <a...@zeit.io> writes: > >>> When an instance method object is created by retrieving a class method >>> object from a class or instance, its __self__ attribute is the class >>> itself, and its __func__ attribute is the function object underlying the >>> class method. >> >> Here I have 2 questions: >> >> 1. How do you create an instance method object from a class method object by >> using either the class or the instance? > > Typically, it happens automatically by accessing "instance.method". > The "types" module contains a type which allows you to > create instance methods manually. However, in this case, > you decide what becomes its "__self__" and its "__function__". > >> 2. Why in both cases the __self__ is set to Class only? > > Because of the "class method". > > The "*method" objects have the task to provide the (implicit) first > argument to the function. For a function defined as "classmethod", > this is the class (otherwise the instance). > >> 3. Would you give me examples also while explaining this? > > python3 >>>> class C: > ... @classmethod > ... def cm(cls): print(cls) > ... def im(self): print(self) > ... >>>> C.cm > <bound method C.cm of <class '__main__.C'>> >>>> c=C() >>>> c.cm > <bound method C.cm of <class '__main__.C'>> >>>> c.im > <bound method C.im of <__main__.C object at 0xb785258c>> >>>> C.cm.__self__ > <class '__main__.C'> >>>> c.cm.__self__ > <class '__main__.C'> >>>> c.im.__self__ > <__main__.C object at 0xb785258c> > >>> When an instance method object is derived from a class method object, the >>> “class instance” stored in __self__ will actually be the class itself, so >>> that calling either x.f(1) or C.f(1) is equivalent to calling f(C,1) where >>> f is the underlying function. > > I agree that the above paragraph could be improved. > > It addresses the case "cm" above: you access a method > defined as a class method (the "is derived from a class method object" above > means "is created for the access to a class method"). > The paragraph wants to stress that even though the (bound method) attribute > is named "__self__", it actually contains the class and not a > (class) instance. > > >> Here x is an instance of C. Would you give me an example to illustrate why " >> x.f(1) or C.f(1) is equivalent to calling f(C,1)” ? > > Remember that the purpose of the "*method" objects it to automatically > provide the first argument ("cls" or "self") to the function. > > Because accessing a method automatically creates a method > object, it is non trivial to access the "underlying function". > One possibility is to use "__func__" on the method object. > With this in mind we get for the above example: > >>>> c.cm.__func__(C) > <class '__main__.C'> >>>> c.cm() > <class '__main__.C'> >>>> C.cm.__func__(C) > <class '__main__.C'> >>>> C.cm() > <class '__main__.C'> > > -- > https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
