Hrvoje Niksic wrote:
Campbell Barton cbarton@metavr.com writes:
pyfloat = PyNumber_Float(value);It might be a good idea to return -1 immediately if this returns NULL. That way you prevent clobbering the real exception with an "invalid argument" exception returned by PyFloat_AsDouble. I think your right, whats there should work but it could return -1 early.
If PyNumber_Float succeeds, but pyfloat turns out not to be float, then the invalid argument exception is perfectly fine.
Is this possible? - if its a number type I would have thaught it must be able to be converted to a float.
However Im wondering if this is advisable, with PyErr_Occurred() its possible that some other part of the API (even a totaly separate API) sets the error string but dosnt return an error value. - Any suggestions?
Requiring the caller to check for PyErr_Occurred seems like bad style, but I'm not sure that it's an actual problem, as long as it's clearly documented.
Lots of Pythons internal code and modules do this. see hows PyFloat_AsDouble's used in cfield.c, _struct.c, datetimemodule.c, selectmodule.c, socketmodule.c..... and others but look in those to see that its used. It looked like bad coding style to me too.
As far as I know, no part of the API is allowed to set the error string and not return an error value because that breaks other parts of Python. Consider this function:
static PyObject * test() { PyErr_SetString(PyExc_TypeError, "test"); Py_INCREF(Py_None); return Py_None; }
Calling it subtly breaks Python:
import foo foo.test() import sys Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: test
The exception lingered until the first function that relies on PyErr_Occurred() to test for an exception, in this case PyImport_*.
your example will mess things up but the way the API works (it seems), is you have functions to work around this and return the correct error values with functions that interface python.
PyFloat_AsDouble - assumes the type is a PyFloat, if its not compatible it WILL set the error string and leaves the API to see if the error string is set and return an error value (-1 or NULL depending on the type of function).