First day with flexx, trying to invoke py method from JS

remote_python.py

from flexx import flx

class RootUI(flx.Widget): # Using Widget as this should hold the UI!

    def init(self, rpy):
        super().init()
        self.rpy = rpy # Capture the remote-python side
        with flx.VBox():
            with flx.HBox():
                self.filename = flx.LineEdit(placeholder_text='foo.txt')
                self.filecontent = flx.LineEdit(placeholder_text='Hello cruel world')
            with flx.HBox():
                self.but = flx.Button(text='Reset')
                self.btnWrite = flx.Button(text='Write')
                self.label = flx.Label(flex=1)

    @flx.reaction('filename.text', 'filecontent.text')
    def greet(self, *events):
        self.label.set_text('hi ' + self.filename.text + ' ' + self.filecontent.text)

    @flx.reaction('but.pointer_click')
    def reset(self, *events):
        self.label.set_text('')

    @flx.reaction('btnWrite.pointer_click')
    def remote_write(self, *events):
        self.rpy.write(self.filename, self.filecontent) # Call write method in remote-python

class Rpy(flx.Component):

    def init(self):
        pass

    def write(self, fname, fcontent):
        with open(fname, 'w') as f:
            f.write(fcontent)
            print("WROTE!!!")

rpy = Rpy()

if __name__ == '__main__':
    a = flx.App(RootUI(rpy)) # Pass a remote python object
    a.serve()
    flx.start()