def request( self, slicing, through=None ):
     assert is_pure_slicing(slicing)
     assert is_bounded(slicing)
     shape = slicing2shape(slicing)
     result = np.zeros( shape, dtype = self._dtype )
     result[:] = self._constant
     return ConstantRequest( result )

 def request( self, slicing ):
     if cfg.getboolean('pixelpipeline', 'verbose'):
         volumina.printLock.acquire()
         print "  LazyflowSource '%s' requests %s" % (self.objectName(), volumina.strSlicing(slicing))
         volumina.printLock.release()
     if not is_pure_slicing(slicing):
         raise Exception('LazyflowSource: slicing is not pure')
     assert self._op5 is not None, "Underlying operator is None.  Are you requesting from a datasource that has been cleaned up already?"
     return LazyflowRequest( self._op5, slicing, self._priority, objectName=self.objectName() )

 def request( self, slicing ):
     if cfg.getboolean('pixelpipeline', 'verbose'):
         volumina.printLock.acquire()
         print "  LazyflowSource '%s' requests %s" % (self.objectName(), volumina.strSlicing(slicing))
         volumina.printLock.release()
     if not is_pure_slicing(slicing):
         raise Exception('LazyflowSource: slicing is not pure')
     if self._outslot.meta.shape is not None:
         reqobj = self._outslot[slicing].allocate(priority = self._priority)        
     else:
         reqobj = ArrayRequest( np.zeros(slicing2shape(slicing), dtype=np.uint8 ), slicing )
     return LazyflowRequest( reqobj )

    def request(self, slicing):
        if not is_pure_slicing(slicing):
            raise Exception("ArraySource: slicing is not pure")
        assert len(slicing) == len(
            self._array.shape
        ), "slicing into an array of shape=%r requested, but slicing is %r" % (self._array.shape, slicing)
        a = ArrayRequest(self._array, slicing)
        a = a.wait()

        # oldDtype = a.dtype
        if self._relabeling is not None:
            a = self._relabeling[a]
        # assert a.dtype == oldDtype
        return ArrayRequest(a, 5 * (slice(None),))

    def setDirty( self, slicing ):
        '''Mark a region of the image as dirty.

        slicing -- if one ore more slices in the slicing
                   are unbounded, the whole image is marked dirty;
                   since an image has two dimensions, only the first
                   two slices in the slicing are used

        '''
        if not is_pure_slicing(slicing):
            raise Exception('dirty region: slicing is not pure')
        if not is_bounded( slicing ):
            self.isDirty.emit(QRect()) # empty rect == everything is dirty
        else:
            self.isDirty.emit(slicing2rect( slicing ))

 def setDirty( self, slicing):
     if not is_pure_slicing(slicing):
         raise Exception('dirty region: slicing is not pure')
     self.isDirty.emit( slicing )