C extension type gives type error in power operator

[Thomas Heller]

Paul Moore schrieb:
> I'm trying to implement an extension type with a power operator. The
> operator is unusual in that I want to allow my objects to be raised to
> an integer power:
> 
>    p = Pattern()
>    p3 = p ** 3
> 
> I've implemented the code for a nb_power slot, it converts the "other"
> argument to a C long using PyInt_AsLong().
> 
> static PyObject *
> Pattern_pow (PyObject *self, PyObject *other, PyObject *modulo)
> {
>     long n = PyInt_AsLong(other);
>     ...
>     /* Ignore modulo argument - not meaningful */
> 
>     if (n == -1 && PyErr_Occurred())
>         return NULL;
> ...
> }
> 
> However, when I try to use the operator, I get the following error:
> TypeError: unsupported operand type(s) for ** or pow():
> '_ppeg.Pattern' and 'int'

Try to set Py_TPFLAGS_CHECKTYPES in your extension type (in the tp_flags slot).

from object.h:
  /* PyNumberMethods do their own coercion */
  #define Py_TPFLAGS_CHECKTYPES (1L<<4)

> I'm not sure where this error is coming from, as I don't have any type
> checks in my code. Is there something else I should add to allow mixed-
> type operations? (This is Python 2.5, if it matters).
> 
> Oh, and is there a good reference for writing C extensions for Python
> anywhere? The manuals aren't bad, but I keep hitting empty sections
> (e.g., 10.5 Number Object Structures).

I normally look into the newest python reference manual, even if I'm
programming for older versions.  But sometimes you have to took into
the header files, too.

Thomas