On Feb 7, 4:10 pm, Berteun Damman <[EMAIL PROTECTED]> wrote: > Hello, > > I was wondering a bit about the differences between methods and > functions. I have the following: > > def wrap(arg): > print type(arg) > return arg > > class C: > def f(): > pass > > @wrap > def g(): > pass > > def h(): > pass > > print type(C.f) > print type(h) > > Which gives the following output: > <type 'function'> > <type 'instancemethod'> > <type 'function'> > > The first line is caused by the 'wrap' function of course. I had > expected the first line to be 'instancemethod' too. So, I would guess, > these methods of C are first created as functions, and only then become > methods after they are 'attached' to some classobj. (You can do that > yourself of course, by saying, for example, C.h = h, then the type of > C.h is 'instancemethod' too.) > > Why does the wrapping occur before the function is 'made' into an > instancemethod?
Consider this: >>> class Foo(object): ... def bar(self): pass ... >>> Foo.bar <unbound method Foo.bar> >>> Foo.__dict__['bar'] <function bar at 0x7d5b0> >>> It shows that when Foo.bar is evaluated, a new instancemethod object is created and that the 'bar' in the dictionary of 'Foo' is forever a plain function object. In fact, Foo.bar is equivalent to Foo.__dict__['bar'].__get__(None, Foo): >>> Foo.__dict__['bar'].__get__(None, Foo) <unbound method Foo.bar> >>> For more details you can read http://users.rcn.com/python/download/Descriptor.htm. > The reason for asking is that I would like to differentiate between > wrapping a function and an instancemethod, because in the latter case, > the first parameter will be the implicit 'self', which I would like to > ignore. However, when the wrapping occurs, the method still looks like > a function. > > Berteun I think you're better off having a 'wrap' decorator for functions and a 'wrapmethod' decorator for methods. HTH -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
