[Python-Dev] __index__ clipping

[Travis E. Oliphant]

Here is my C-API proposal

1) PyIndex_Check(obj)

   Similar to PyIter_Check(obj) as it just checks for whether or not the 
object can call nb_index.  Actually implemented as a macro.

2) PyObject* PyNumber_Index(obj)

   Simple interface around nb_index that calls it if possible and returns
   TypeError if not (or if the result does not end up in an exact
   int-or-long

3) Py_ssize_t PyNumber_AsSsize_t(obj, err)

    This converts the object to a Py_ssize_t by using the nb_index call
    if possible.  The err argument is a Python error object and specifies
    what error should be raised should the conversion from Int-or-Long to
    Py_ssize_t cause Overflow.

    If err is NULL, then no error will be raised and the result will be 
clipped.  Other-wise the corresponding error will be set.  Internally 
PyExc_IndexError and PyExc_OverflowError will be the errors used.


-Travis