[Mapserver-users] python mapscript
Sean Gillies
sgillies at frii.com
Wed Jul 2 11:55:42 PDT 2003
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On Wednesday, July 2, 2003, at 11:58 AM, Steve Lime wrote:
> MapServer query functions do return an error (MS_FAILURE) but also set
> the error code to MS_NOTFOUND so that folks can trap that condition
> specifically in their application. The CGI does that using the EMPTY
> web
> parameter. Yes, you could change the return status to MS_SUCCESS, but
> either way you'd have to examine the error code to see if no records
> were found (or worse the result set itself). It seems more intuitive to
> me to encourage that check by returning MS_FAILURE.
>
> Steve
>
> Stephen Lime
> Data & Applications Manager
>
>
Michael,
Try replacing pymodule.i in your mapscript/python directory with the
one I've attached to this email. It implements a new Python exception
named 'MapServerNotFoundError' which will be raised when MapServer
throws a MS_NOTFOUND error in queryByPoint(). I chose this name
because 'NotFoundError' is too ambiguous and MS_NOTFOUNDError doesn't
look like a Python exception. In the future, we could add exceptions
like 'MapServerGDError' etc.
To use it, you'll do
try:
queryByPoint()
except MapServerNotFoundError:
# No records found
...
If it works, I'll commit it to CVS. I still think that msQueryByPoint
shouldn't throw an error when there are no records, but that the
application itself should check the returned record set. We'll work
this out one way or the other before 4.1.
cheers,
Sean
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name="pymodule.i"
/******************************************************************************
* $Id: pymodule.i,v 1.3 2003/06/17 04:34:07 sean Exp $
*
* Project: MapServer
* Purpose: Python-specific enhancements to MapScript
* Author: Sean Gillies, sgillies at frii.com
*
******************************************************************************
*
* Python-specific mapscript code has been moved into this
* SWIG interface file to improve the readibility of the main
* interface file. The main mapscript.i file includes this
* file when SWIGPYTHON is defined (via 'swig -python ...').
*
*****************************************************************************/
/******************************************************************************
* Supporting 'None' as an argument to attribute accessor functions
******************************************************************************
*
* Typemaps to support NULL in attribute accessor functions
* provided to Steve Lime by David Beazley and tested for Python
* only by Sean Gillies.
*
* With the use of these typemaps and some filtering on the mapscript
* wrapper code to change the argument parsing of *_set() methods from
* "Os" to "Oz", we can execute statements like
*
* layer.group = None
*
*****************************************************************************/
#ifdef __cplusplus
%typemap(memberin) char * {
if ($1) delete [] $1;
if ($input) {
$1 = ($1_type) (new char[strlen($input)+1]);
strcpy((char *) $1,$input);
} else {
$1 = 0;
}
}
%typemap(memberin,warning="451:Setting const char * member may leak
memory.") const char * {
if ($input) {
$1 = ($1_type) (new char[strlen($input)+1]);
strcpy((char *) $1,$input);
} else {
$1 = 0;
}
}
%typemap(globalin) char * {
if ($1) delete [] $1;
if ($input) {
$1 = ($1_type) (new char[strlen($input)+1]);
strcpy((char *) $1,$input);
} else {
$1 = 0;
}
}
%typemap(globalin,warning="451:Setting const char * variable may leak
memory.") const char * {
if ($input) {
$1 = ($1_type) (new char[strlen($input)+1]);
strcpy((char *) $1,$input);
} else {
$1 = 0;
}
}
#else
%typemap(memberin) char * {
if ($1) free((char*)$1);
if ($input) {
$1 = ($1_type) malloc(strlen($input)+1);
strcpy((char*)$1,$input);
} else {
$1 = 0;
}
}
%typemap(memberin,warning="451:Setting const char * member may leak
memory.") const char * {
if ($input) {
$1 = ($1_type) malloc(strlen($input)+1);
strcpy((char*)$1,$input);
} else {
$1 = 0;
}
}
%typemap(globalin) char * {
if ($1) free((char*)$1);
if ($input) {
$1 = ($1_type) malloc(strlen($input)+1);
strcpy((char*)$1,$input);
} else {
$1 = 0;
}
}
%typemap(globalin,warning="451:Setting const char * variable may leak
memory.") const char * {
if ($input) {
$1 = ($1_type) malloc(strlen($input)+1);
strcpy((char*)$1,$input);
} else {
$1 = 0;
}
}
#endif // __cplusplus
/**************************************************************************
* MapServer Errors and Python Exceptions
**************************************************************************
*
* Translation of errors reported via the ms_error structure into
* Python exceptions. Original code by Chris Chamberlin <cdc at aracnet.com>
* has been updated by Sean Gillies <sgillies at frii.com> to use
* PyErr_SetString, %exception and $action for SWIG 1.3, do the most
* obvious mapping of MapServer errors to Python exceptions and map all
* others to a new 'MapservError' exception which can be caught like this:
*
* from mapscript import *
* empty_map = mapObj('')
* try:
* img = empty_map.draw()
* except MapservError, msg:
* print "Caught MapservError:", msg
*
*************************************************************************/
%{
PyObject *MSExc_MapservError;
PyObject *MSExc_MapServerNotFoundError;
%}
%init %{
// Generic MapServer error
MSExc_MapservError = PyErr_NewException("_mapscript.MapservError", NULL, NULL);
if (MSExc_MapservError != NULL)
PyDict_SetItemString(d, "MapservError", MSExc_MapservError);
// MapServer query MS_NOTFOUND error
MSExc_MapServerNotFoundError = PyErr_NewException("_mapscript.MapServerNotFoundError", NULL, NULL);
if (MSExc_MapServerNotFoundError != NULL)
PyDict_SetItemString(d, "MapServerNotFoundError", MSExc_MapServerNotFoundError);
%}
%{
static void _raise_ms_exception(void) {
char errbuf[256];
char errmsg[2048]; // room for up to 8 * 256 byte messages
int errcode;
errorObj *ms_error;
strcpy(errmsg, "");
ms_error = msGetErrorObj();
errcode = ms_error->code;
// Step through the error list, appending to the output error
// message.
while (ms_error && ms_error->code > 0) {
snprintf(errbuf, 255, "%s: %s %s\n", ms_error->routine,
msGetErrorString(ms_error->code), ms_error->message);
strcat(errmsg, errbuf);
ms_error = ms_error->next;
}
// Map MapServer errors to Python exceptions, will define
// custom Python exceptions soon. The exception we raise
// is based on the error at the head of the MapServer error
// list. All other errors appear in the error message.
switch (errcode) {
case MS_IOERR:
PyErr_SetString(PyExc_IOError, errmsg);
break;
case MS_MEMERR:
PyErr_SetString(PyExc_MemoryError, errmsg);
break;
case MS_TYPEERR:
PyErr_SetString(PyExc_TypeError, errmsg);
break;
case MS_EOFERR:
PyErr_SetString(PyExc_EOFError, errmsg);
break;
case MS_NOTFOUND:
PyErr_SetString(MSExc_MapServerNotFoundError, errmsg);
break;
default:
PyErr_SetString(MSExc_MapservError, errmsg);
break;
}
}
%}
%exception {
$action {
errorObj *ms_error = msGetErrorObj();
// Sidestep the annoying MS_IOERR raised by msSearchDiskTree()
// in maptree.c when a layer's shapetree index can't be found
if ((ms_error->code != MS_NOERR) && (ms_error->code != -1)
&& !((ms_error->code == MS_IOERR) &&
(strcmp(ms_error->routine, "msSearchDiskTree()") == 0)))
{
_raise_ms_exception();
// Clear the error list
msResetErrorList();
return NULL;
}
}
}
%pythoncode %{
MapservError = _mapscript.MapservError
MapServerNotFoundError = _mapscript.MapServerNotFoundError
%}
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--
Sean Gillies
sgillies at frii dot com
http://www.frii.com/~sgillies
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