C module calls python script: how to set exception in C

[Harald Kirsch]

In my C module I call user (i.e. programmer) supplied python callables
(i.e. those beasts defined with def) like

 str = PyObject_CallObject(callable, args);

If callable fails, it sets the error indicator in the python
interpreter and I let my function return NULL. The net effect is a
nice stack trace denoting the place of failure in the python code
associated with the callable.

However, if the callable does not fail but return a value my function
is not happy with, i.e. it returns an integer object while it is
required to return a string, what is a good way to set up the error
indicator? I expect it to be like

  PyErr_Format(PyExc_TypeError,
               "%s returned wrong value", 
               PyObject_Repr(callable))

However, is it safe to call PyObject_Repr here, or can it itself err
again? (Ah, well and PyObject_Repr actually returns PyObject* and
needs to be converted.)

  Harald Kirsch
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Harald Kirsch   | kirschh at lionbioscience.com | "How old is the epsilon?"
LION bioscience | +49 6221 4038 172          |        -- Paul Erdös
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