[Python-Dev] PEP 203 Augmented Assignment

[Michael Hudson]

Guido van Rossum <guido@beopen.com> writes:

> > Good idea.  Are lists and tuples going to support seq[a:b:c] anytime soon?
> 
> It's on my wish list, but can't be done for 2.0.

This would involve the list type implementing the mapping API wouldn't
it?  This would seem to be a little on the silly side.  Never mind;
here's a quick-hack patch that "seems to work" for lists:

Index: listobject.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/listobject.c,v
retrieving revision 2.83
diff -u -c -r2.83 listobject.c
*** listobject.c	2000/07/25 12:56:38	2.83
--- listobject.c	2000/07/27 20:38:50
***************
*** 1400,1405 ****
--- 1400,1441 ----
  	(objobjproc)list_contains, /*sq_contains*/
  };
  
+ static PyObject*
+ list_subscript(PyObject* list, PyObject* item)
+ {
+ 	if (PyInt_Check(item)) {
+ 		return list_item((PyListObject*)list,PyInt_AS_LONG(item));
+ 	} else if (PySlice_Check(item)) {
+ 		int start, stop, step, cur, i;
+ 		PyObject* result;
+ 		PyObject* it;
+ 
+ 		if (PySlice_GetIndices((PySliceObject*)item,PyList_Size(list),&start,&stop,&step) < 0) {
+ 			PyErr_SetString(PyExc_TypeError, "slice indices must be integers");
+ 			return NULL;
+ 		}
+ 
+ 		result = PyList_New((stop-start)/step+1);
+ 
+ 		for (cur = start, i = 0; cur < stop; cur += step, i++) {
+ 			it = PyList_GET_ITEM(list,cur);
+ 			Py_INCREF(it);
+ 			PyList_SET_ITEM(result,i,it);
+ 		}
+ 
+ 		return result;
+ 	} else {
+ 		PyErr_SetString(PyExc_TypeError, "list indices must be integers");
+ 		return NULL;
+ 	}
+ };
+ 
+ static PyMappingMethods list_as_mapping = {
+ 	(inquiry)list_length,
+ 	(binaryfunc)list_subscript,
+ 	(objobjargproc)NULL
+ };
+ 
  PyTypeObject PyList_Type = {
  	PyObject_HEAD_INIT(&PyType_Type)
  	0,
***************
*** 1414,1420 ****
  	(reprfunc)list_repr, /*tp_repr*/
  	0,		/*tp_as_number*/
  	&list_as_sequence,	/*tp_as_sequence*/
! 	0,		/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
  	0,		/*tp_str*/
--- 1450,1456 ----
  	(reprfunc)list_repr, /*tp_repr*/
  	0,		/*tp_as_number*/
  	&list_as_sequence,	/*tp_as_sequence*/
! 	&list_as_mapping,	/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
  	0,		/*tp_str*/

Have I missed anything obvious?  I'd upload it to SF, but I don't
really want something I've put such little effort into to be seriously
considered...

Cheers,
M.

-- 
112. Computer Science is embarrassed by the computer.
  -- Alan Perlis, http://www.cs.yale.edu/homes/perlis-alan/quotes.html