On 10/15/2013 09:10 PM, Even Rouault wrote:
Martin,
The closest equivalent in the GDAL/OGR code base I could think of is the
possibility of defining a custom error handler from the Python bindings.
For the Perl bindings I wrote a mechanism to call a Perl function via
the GDALProgressFunc mechanism, which is used quite a lot - it was a bit
like dark art, but seems to work. Is similar implemented for Python?
Ari
Basically you would need to have a C API to register a C callback,
"VFKLineCallbackRegister", and you would have a Python C module that would
define such a C callback "PyVFKCallbackWrapper" (or extend the existing GDAL
Python bindings), that would be a wrapper that would take a Python callable
object as argument and call it. And you would have a C function, exposed as
Python, "RegisterVFKCallback" that would pass PyVFKCallbackWrapper to
VFKLineCallbackRegister with the Python function as a userdata.
The relevant existing code is in :
* swig/include/port.i :
/* Equivalent of PyVFKCallbackWrapper */
%{
void CPL_STDCALL PyCPLErrorHandler(CPLErr eErrClass, int err_no, const char*
pszErrorMsg)
{
void* user_data = CPLGetErrorHandlerUserData();
PyObject *psArgs;
psArgs = Py_BuildValue("(iis)", eErrClass, err_no, pszErrorMsg );
PyEval_CallObject( (PyObject*)user_data, psArgs);
Py_XDECREF(psArgs);
}
%}
/* Equivalent of RegisterVFKCallback */
%inline %{
CPLErr PushErrorHandler( CPLErrorHandler pfnErrorHandler = NULL, void*
user_data = NULL )
{
[...]
CPLPushErrorHandlerEx(pfnErrorHandler, user_data); /* equivalent of
VFKLineCallbackRegister */
return CE_None;
}
%}
* swig/include/python/typemaps_python.i :
%typemap(in) ( CPLErrorHandler pfnErrorHandler = NULL, void* user_data = NULL
)
{
/* %typemap(in) (CPLErrorHandler pfnErrorHandler = NULL, void* user_data =
NULL) */
[...]
if (!PyCallable_Check($input))
{
PyErr_SetString( PyExc_RuntimeError,
"Object given is not a String or a Python function"
);
SWIG_fail;
}
else
{
Py_INCREF($input);
$1 = PyCPLErrorHandler;
$2 = $input;
}
}
Best regards,
Even
Hi all,
I wonder if there is a way how to implement mechanism for
user-specified events and handlers in GDAL/OGR.
I am implementing a Python script which checks VFK file using OGR
driver [1]. This script reads VFK data and stores them in SQLite
database which is created by the OGR driver.
Beside some geometry checks the script should do some extra
user-defined checks on the original VFK file. To avoid double reading
of the file (first by the script and then by the OGR driver) I would
like to use mechanism of events and handlers. In other words, event
for reading a new line from the VFK file [2] and the handler (callback
subroutine in Python script) which would do some extra checks on the
line [3].
Any idea how it should be correctly implemented in VFK driver and the
Python script? Thanks a lot for any hits in advance!
Martin
[1] http://gdal.org/ogr/drv_vfk.html
[2]
http://trac.osgeo.org/gdal/browser/trunk/gdal/ogr/ogrsf_frmts/vfk/vfkreade
r.cpp#L125 [3]
https://github.com/landam/ogr-vfk-testing/blob/master/read-vfk-test/read-v
fk.py#L52
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