def verifyTargets(self):
        """
        Used in backprop() to verify that the network targets have
        been set.
        """
        for layer in self.layers:
            if layer.verify and layer.type == 'Output' and layer.active and not layer.targetSet:
                raise LayerError('Targets are not set and verifyTargets() was called.',\
                                   (layer.name, layer.type))
            else:
                layer.resetTargetFlag()