[Python-Dev] Let's get rid of unbound methods

[Guido van Rossum]

In my blog I wrote:

Let's get rid of unbound methods. When class C defines a method f, C.f
should just return the function object, not an unbound method that
behaves almost, but not quite, the same as that function object. The
extra type checking on the first argument that unbound methods are
supposed to provide is not useful in practice (I can't remember that
it ever caught a bug in my code) and sometimes you have to work around
it; it complicates function attribute access; and the overloading of
unbound and bound methods on the same object type is confusing. Also,
the type checking offered is wrong, because it checks for subclassing
rather than for duck typing.

This is a really simple change to begin with:

*** funcobject.c	28 Oct 2004 16:32:00 -0000	2.67
--- funcobject.c	4 Jan 2005 18:23:42 -0000
***************
*** 564,571 ****
  static PyObject *
  func_descr_get(PyObject *func, PyObject *obj, PyObject *type)
  {
! 	if (obj == Py_None)
! 		obj = NULL;
  	return PyMethod_New(func, obj, type);
  }
  
--- 564,573 ----
  static PyObject *
  func_descr_get(PyObject *func, PyObject *obj, PyObject *type)
  {
! 	if (obj == NULL || obj == Py_None) {
! 		Py_INCREF(func);
! 		return func;
! 	}
  	return PyMethod_New(func, obj, type);
  }
  
There are some test suite failures but I suspect they all have to do
with checking this behavior.

Of course, more changes would be needed: docs, the test suite, and
some simplifications to the instance method object implementation in
classobject.c.

Does anyone think this is a bad idea? Anyone want to run with it?

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)