[vtkusers] Python observer handling

[Willi Huber]

Hello all,

I know exception handling in VTK has been discussed quite a while so I don't want to add insult to an injury.

Since David Gobbi very often posted his code:
==== python code ====
import vtk class ErrorObserver:    def __init__(self):
       self.__ErrorOccurred = False
       self.__ErrorMessage = None
       self.CallDataType = 'string0'    def __call__(self, obj, event, message):
       self.__ErrorOccurred = True
       self.__ErrorMessage = message    def ErrorOccurred(self):
       occ = self.__ErrorOccurred
       self.__ErrorOccurred = False
       return occ    def ErrorMessage(self):
       return self.__ErrorMessage e = ErrorObserver() a = vtk.vtkImageReader()
a.AddObserver('ErrorEvent', e) print "doing update"
a.Update()
if e.ErrorOccurred():
   print e.ErrorMessage()
==== python code ====

Unfortunately it is not working as intended. I tried this code which obviously had to fail:

==== python code ====
mapper = vtk.vtkPolyDataMapper()
mapper.AddObserver('ErrorEvent', e)
mapper.SetInputConnection(reader.GetOutputPort()) #reader is of type vtkMetaImageReader
mapper.Update()

if e.ErrorOccurred():
   print e.ErrorMessage()
else:
   print "No Error"
==== python code ====
but it didn't. Now I know about this error but I am still curious why it was not working as intended.
Shouldn't it print the cause of the error rather than "No Error"?

Everytime I tried this code a vtk warning window poped up which can't be read since the whole application dies with some Windows failure handling. Therefore I was not able to read the error message in the window and had a tough time finding out about the problem. Uncommenting renWin.Render() let me read the error.
Any suggestions what I am doing wrong?


Cheers,
Willi
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