By writing a small demo to complete my post, I found the issue. As it might be helpful to somebody else, here it is:

demo.scxml:

<?xml version="1.0" encoding="UTF-8"?> <scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" binding="early" xmlns:qt="http://www.qt.io/2015/02/scxml-ext" name="plop.scxml" qt:editorversion="4.7.1"> <state id="State_1"> <qt:editorinfo scenegeometry="144.50;162.05;84.50;112.05;120;100" geometry="144.50;162.05;-60;-50;120;100"/> </state> </scxml>

demo.py:

#!/usr/bin/env python import sys from PySide2.QtCore import QObject, QCoreApplication, SLOT, Slot from PySide2.QtScxml import QScxmlStateMachine class Backend_1(QObject): def __init__(self, machine): super(Backend_1, self).__init__() self.machine = machine self.machine.connectToState("State_1", self, SLOT("s1_active(bool)")) @Slot(bool) def s1_active(self, active): if active: print('Backend_1::State_1: enter') self.submachine = QScxmlStateMachine.fromFile('demo.scxml') b = Backend_2(self.submachine) self.submachine.start() else: print('Backend_1::State_1: exit') class Backend_2(QObject): def __init__(self, machine): super(Backend_2, self).__init__() self.machine = machine self.machine.connectToState("State_1", self, SLOT("s1_active(bool)")) @Slot(bool) def s1_active(self, active): if active: print('Backend_2::State_1: enter') else: print('Backend_2::State_1: exit') if __name__ == '__main__': app = QCoreApplication(sys.argv) machine = QScxmlStateMachine.fromFile('demo.scxml') b = Backend_1(machine) machine.start() sys.exit(app.exec_())

If you run this, you expect to see:
Backend_1::State_1: enter
Backend_2::State_1: enter

But, the second statemachine does not seem to start. To fix it, you need to store the instance of Backend_2 (eg: self.b = Backend_2(self.submachine)). I guess it was garbage collected, so all the states/events connections were broken.

Meanwhile, if you think my design patter is bad, I'm willing to learn :)

@nurettin I see, gettting the scxml + js outside the application seems more versatile

I got a hint on stackoverflow

Could it be possible you provide a link to such Q&A for anybody interested? Thanks

Hi,

The QtSCXML module being currently a technical preview, you should bring your questions to the interest mailing list. You'll find there QtSCXML's developers/maintainers. This forum is more user oriented and there's likely less people having already used that module here.

Hi and welcome to devnet,

The QtSCXML module being currently a technical preview, you should bring your questions to the interest mailing list. You'll find there QtSCXML's developers/maintainers. This forum is more user oriented and there's likely less people having already used that module here.

Answered on StackOverflow. The key is that there are many functions hidden from the documentation that need to be overridden, like evaluateToString().