C extension module doesn't throw exception after setting error indicator through PyErr_SetString()

Tim Golden mail at timgolden.me.uk
Thu Aug 2 11:06:29 CEST 2012

On 02/08/2012 09:57, rahul wrote:
> I am implementing a C extension module, during this I saw that when I
> set the global error indicator and error message through
> PyErr_SetString() API and return false.
> But it doesn't throw any error when I tried to check the error
> through sys.exc_info() then it returns (NULL, NULL, NULL) tuple.
> When I return NULL through the C extension module's function then it
> works correctly and throws the exception as expected.
> The skeleton looks like:
> static PyObject* check(PyObject* sef, PyObject* args) { PyObject*
> input = NULL; if (!PyArg_ParseTuple(args, "O", &input)){ return
> NULL; } ..... ..... PyErr_SetString(PyExc_Exception, "Throwing Error
> through check function"); Py_RETURN_FALSE; }
> Any idea on why this is happening? Any help will be appreciated.

Because you're returning False. You should be returning NULL. Which is
why it works when you do :)

Have a look at the first line of this page:


Which piece of documentation led you to think that returning False was
the thing to do here? Perhaps there's a doc that needs fixing?


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