import hou
import viewerstate.utils as su

class State(object):
    def __init__(self, state_name, scene_viewer):
        self.state_name = state_name
        self.scene_viewer = scene_viewer

    def onStopSelection(self, kwargs):
        """ Called when a bound selector has been terminated
        """
        selector_name = kwargs["name"]
        self.log(selector_name + " has stopped")
        self.scene_viewer.enterViewState()           # my modification

    def onSelection(self, kwargs):
        """ Called when a selector has selected something
        """        
        selection = kwargs["selection"]

        self.log(selection)

        # Return False to keep the selector active or True to stop it.
        return False

    def onStartSelection(self, kwargs):
        """ Called when a bound selector has been started
        """
        selector_name = kwargs["name"]
        self.log(selector_name + " has started")


    def onExit(self,kwargs):
        """ Called when the state terminates
        """
        state_parms = kwargs["state_parms"]
        print('onExit')


def createViewerStateTemplate():
    """ Mandatory entry point to create and return the viewer state 
        template to register. """

    state_typename = kwargs["type"].definition().sections()["DefaultState"].contents()
    state_label = "Tomek::dev::testingstate::1.0"
    state_cat = hou.sopNodeTypeCategory()

    template = hou.ViewerStateTemplate(state_typename, state_label, state_cat)
    template.bindFactory(State)
    template.bindIcon(kwargs["type"].icon())


    # The selector will start when the state enters
    template.bindGeometrySelector("SOP: Select a primitive", quick_select=True, name="My Primitive Selector")


    return template

...
    def onKeyEvent(self, kwargs):
        ui_event = kwargs['ui_event']
        if(ui_event.device().keyString() == "Enter"):
            self.scene_viewer.setCurrentState("curve::2.0")

import hdefereval
hdefereval.executeDeferred(deferEnterViewState, self.scene_viewer)

def deferEnterViewState(scene_viewer):
   scene_viewer.enterViewState()

$HH/python3.9libs/hdefereval.py