Many classes of screens with repeated functions | How do I create a function for all classes?

[Felipe Viera]

Hello! I made an app with several classes of screens with repeated codes:

class screen1(Screen):
    def on_pre_enter(self):
        Window.bind(on_keyboard=self.voltar)
    def voltar(self, window, key, *args):
        if key == 27:
            MDApp.get_running_app().root.transition.direction = 'right'
            MDApp.get_running_app().root.current = 'menu'
            return True
    def on_pre_leave(self):
        Window.unbind(on_keyboard=self.voltar)

class screen2(Screen):
    def on_pre_enter(self):
        Window.bind(on_keyboard=self.voltar)
    def voltar(self, window, key, *args):
        if key == 27:
            MDApp.get_running_app().root.transition.direction = 'right'
            MDApp.get_running_app().root.current = 'menu'
            return True
    def on_pre_leave(self):
        Window.unbind(on_keyboard=self.voltar)

class screen3(Screen):
    def on_pre_enter(self):
        Window.bind(on_keyboard=self.voltar)
    def voltar(self, window, key, *args):
        if key == 27:
            MDApp.get_running_app().root.transition.direction = 'right'
            MDApp.get_running_app().root.current = 'menu'
            return True
    def on_pre_leave(self):
        Window.unbind(on_keyboard=self.voltar)

# 18 screens...

And I want to copy the functions of one screen and paste in all others to decrease the code:

class ScreenClass():
    def on_pre_enter(self):
        Window.bind(on_keyboard=self.voltar)
    def voltar(self, window, key, *args):
        if key == 27:
            MDApp.get_running_app().root.transition.direction = 'right'
            MDApp.get_running_app().root.current = 'menu'
            return True
    def on_pre_leave(self):
        Window.unbind(on_keyboard=self.voltar)

class screen1(Screen):
    ScreenClass.on_pre_enter()
    ScreenClass.voltar()
    ScreenClass.on_pre_leave()

class screen2(Screen):
    ScreenClass.on_pre_enter()
    ScreenClass.voltar()
    ScreenClass.on_pre_leave()

class screen3(Screen):
    ScreenClass.on_pre_enter()
    ScreenClass.voltar()
    ScreenClass.on_pre_leave()

But I get an error, I also tried using @classmethod, but it returns an error. I tried many ways, when I don't get an error, the functions don't work :(

[Robert Flatt]

That should be     ScreenClass(Screen) :

Then just use ScreenClass()  everywhere you use screen1() , screen2() , screen3()

Forget screen1() , screen2() , screen3()

Because you can have more than one instance of a Class.

[Felipe Viera]

Thank you Robert! The functions did not work,

but I managed with:

class screen1(ScreenClass):
    pass

class screen2(ScreenClass):
    pass

class screen3(ScreenClass):
    pass