How to catch a usefull error message ?
Vincent Vande Vyvre
vincent.vande.vyvre at telenet.be
Wed Apr 24 14:46:57 EDT 2019
Le 24/04/19 à 19:57, MRAB a écrit :
> 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.
In this case yes, beause it need to return the result of the command system.
But the "return 0" is a common case for an "Foo_init()"
see:
https://docs.python.org/3.5//extending/newtypes.html#adding-data-and-methods-to-the-basic-example
... And that's nothing to do with my initial question
Vincent
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