> On Sun, Feb 04, 2001 at 11:47:26PM -0500, Guido van Rossum wrote:
> > Yes, I've often thought that we should be able to heal the split for
> > 95% by using a few well-aimed tricks like this. Later...
>
> I was playing around this weekend with the class/type problem.
> Without too much effort I had an interpreter that could to things
> like this:
>
> >>> class MyInt(type(1)):
> ... pass
> ...
> >>> i = MyInt(10)
> >>> i
> 10
> >>> i + 1
> 11
Now, can you do things like this:
>>> from types import *
>>> class MyInt(IntType): # add a method
def add1(self): return self+1
>>> i = MyInt(10)
>>> i.add1()
11
>>>
and like this:
>>> class MyInt(IntType): # override division
def __div__(self, other): return float(self) / other
def __rdiv__(self, other): return other / float(self)
>>> i = MyInt(10)
>>> i/3
0.33333333333333331
>>>
I'm not asking for adding new instance variables (slots), but that of
course would be the next step of difficulty up.
> The major changes were allowing PyClassObject to subclass types
> (ie. changing PyClass_Check(op) to (PyClass_Check(op) ||
> PyType_Check(op))), writing a _PyType_Lookup function, and making
> class_lookup use it.
Yeah, but that's still nasty. We should strive for unifying PyClass
and PyType instead of having both around.
> The experiment has convinced me that we can allow subclasses of
> types quite easily without major changes. It has also given me
> some ideas on "the right way" to solve this problem. The rough
> scheme I can up yesterday goes like this:
>
p> PyObject {
> int ob_refcnt;
> PyClass ob_class;
(plus type-specific fields I suppose)
> }
>
> PyClass {
> PyObject_HEAD
> char *cl_name;
> getattrfunc cl_getattr;
> PyMethodTable *cl_methods;
> }
>
> PyMethodTable {
> binaryfunc nb_add;
> binaryfunc nb_sub;
> ...
> }
>
> When calling a method on a object the interpreter would first
> check for a direct method and if that does not exist then call
> cl_getattr. Obviously there are still a few details to be worked
> out. :-)
Yeah... Like you should be able to ask for ListType.append and get an
unbound built-in method back, which can be applied to a list:
ListType.append([], 1) === [].append(1)
And ditto for operators:
IntType.__add__(1, 2) === 1+2
And a C API like PyNumber_Add(x, y) should be equivalent to using
x.__add__(y), too.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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