How to catch a usefull error message ?
MRAB
python at mrabarnett.plus.com
Wed Apr 24 13:57:06 EDT 2019
On 2019-04-23 20:21, Vincent Vande Vyvre wrote:
> Le 23/04/19 à 20:54, Chris Angelico a écrit :
>> On Wed, Apr 24, 2019 at 4:47 AM Vincent Vande Vyvre
>> <vincent.vande.vyvre at telenet.be> wrote:
>>
>> 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 ?
>> The SystemError means that you're using the Python C API in a way that
>> doesn't make sense to the interpreter. You're leaving a marker saying
>> "hey, I need you to throw an exception" but then you're also returning
>> a value. You'll need to figure out where that's happening and exactly
>> what is being called. How are you setting up your class?
>>
>> ChrisA
>
> The syntaxe
>
> if (!PyArg_ParseTuple(args, "s", &fname))
> return NULL;
>
> Is the usage described in the doc [*]
>
> And without block try-except I get the good one error.
>
>
> [*]
> https://docs.python.org/3.5//extending/extending.html#back-to-the-example
>
If you look at the previous example, the function's return type is
"PyObject *".
On success it returns a reference (pointer) to an object; on error it
returns NULL.
Your function's return type is int.
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