How to catch a usefull error message ?

[Vincent Vande Vyvre]

Le 23/04/19 à 19:23, Chris Angelico a écrit :
> On Wed, Apr 24, 2019 at 3:18 AM Vincent Vande Vyvre
> <vincent.vande.vyvre at telenet.be> wrote:
>> Hi,
>>
>> In a CPython lib I have an _init() method wich take one argument, a file
>> name.
>>
>>       char *fname;
>>
>>       if (!PyArg_ParseTuple(args, "s", &fname))
>>           return NULL;
>>
>> So, if I instanciate my object with a bad argument I've a good error
>> message:
>>
>> tif = ImgProc(123)
>> TypeError: argument 1 must be str, not int
>> (followed by the traceback)
>>
>> But if I do:
>> try:
>>       tif = ImgProc(123)
>> except Exception as why:
>>       print("Error:", why)
>>
>> I get just:
>>
>> Error: <class '_liboqapy.ImgProc'> returned a result with an error set
>>
> It looks like there's an internal problem in the C function. Are you
> sure it's hitting the PyArg_ParseTuple and then immediately returning
> NULL? Post a bit more of your code; this error looks like something is
> leaving an error state but then carrying on with the code.
>
> ChrisA

Into the lib:

static int
ImgProc_init(ImgProc *self, PyObject *args, PyObject *kwds)
{
     PyObject *tmp;
     char *fname;

     if (!PyArg_ParseTuple(args, "s", &fname))
         return NULL;

     tmp = self->src;
     self->src = PyUnicode_FromString(fname);
     Py_XDECREF(tmp);
     return 0;
}

If i do:
     try:
         tif = ImgProc(123)
     except Exception as why:
         print(sys.exc_info())
         raise
I get:
(<class 'SystemError'>, SystemError("<class '_liboqapy.ImgProc'> 
returned a result with an error set",), <traceback object at 
0x7f3bcac748c8>)
TypeError: argument 1 must be str, not int

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
   File "/home/vincent/oqapy-3/trunk/filters/ui_lenscorrection.py", line 
104, in on_main_cursor_changed
     self.prepare_preview_process()
   File "/home/vincent/oqapy-3/trunk/filters/ui_lenscorrection.py", line 
137, in prepare_preview_process
     self.main.process_on_preview(params)
   File "/home/vincent/oqapy-3/trunk/filters/lenscorrection.py", line 
56, in process_on_preview
     tif = ImgProc(123)
SystemError: <class '_liboqapy.ImgProc'> returned a result with an error set
--------------------------------------------------------------------------------
Why a SystemError ?

I'm using Python 3.6.7 and 3.7.3

Vincent