C API PyObject_Call segfaults with string

Thu Feb 10 17:13:21 EST 2022

Thank you for that suggestion.  It allowed me to replace six lines of code with one.  :)
Feb 10, 2022, 12:43 by python at mrabarnett.plus.com:
> On 2022年02月10日 20:00, Jen Kris via Python-list wrote:
>>> With the help of PyErr_Print() I have it solved.  Here is the final code (the part relevant to sents):
>>>>    Py_ssize_t listIndex = 0;
>>    pListItem = PyList_GetItem(pFileIds, listIndex);
>>    pListStrE = PyUnicode_AsEncodedString(pListItem, "UTF-8", "strict");
>>    pListStr = PyBytes_AS_STRING(pListStrE); // Borrowed pointer
>>>>    // Then:  sentences = gutenberg.sents(fileid) - this is a sequence item
>>    PyObject *c_args = Py_BuildValue("s", pListStr);
>>    PyObject *args_tuple = PyTuple_New(1);
>>    PyTuple_SetItem(args_tuple, 0, c_args);
>>>>    pSents = PyObject_CallObject(pSentMod, args_tuple);
>>>>    if ( pSents == 0x0){
>>        PyErr_Print();
>>        return return_value; }
>>>> As you mentioned yesterday, CallObject needs a tuple, so that was the problem.  Now it works.
>>>> You also asked why I don't just use pListStrE.  I tried that and got a long error message from PyErr_Print.  I'm not far enough along in my C_API work to understand why, but it doesn't work.
>>>> Thanks very much for your help on this.
>>> You're encoding a Unicode string to a UTF-8 bytestring:
>> pListStrE = PyUnicode_AsEncodedString(pListItem, "UTF-8", "strict");
>> then pointing to the bytes of that UTF-8 bytestring:
>> pListStr = PyBytes_AS_STRING(pListStrE); // Borrowed pointer
>> then making a Unicode string from those UTF-8 bytes:
>> PyObject *c_args = Py_BuildValue("s", pListStr);
>> You might was well just use the original Unicode string!
>> Try this instead:
>> Py_ssize_t listIndex = 0;
> pListItem = PyList_GetItem(pFileIds, listIndex);
> //> pListItem?
>> pSents = PyObject_CallFunctionObjArgs(pSentMod, pListItem, 0);
> //> pSents+?
>> if (pSents == 0x0){
> PyErr_Print();
> return return_value;
> }
>>>>>>> Feb 9, 2022, 17:40 by songofacandy at gmail.com:
>>>>> On Thu, Feb 10, 2022 at 10:37 AM Jen Kris <jenkris at tutanota.com> wrote:
>>>>>>>>>>> I'm using Python 3.8 so I tried your second choice:
>>>>>>>> pSents = PyObject_CallFunctionObjArgs(pSentMod, pListItem);
>>>>>>>> but pSents is 0x0. pSentMod and pListItem are valid pointers.
>>>>>>>>>> It means exception happened.
>>> If you are writing Python/C function, return NULL (e.g. `if (pSents ==
>>> NULL) return NULL`)
>>> Then Python show the exception and traceback for you.
>>>> -- 
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