back button functionality on android with kivy

Kivy on android binds the back button to the esc button so binding and listening to esc button in your app would help you handle how your app behaves when the back button is pressed.

In other words in your app when testing it on your desktop listen to the escape key from the system keyboard, this will be automatically be translated to being the back button on your android device. Something like::

def on_start():
    from kivy.base import EventLoop
    EventLoop.window.bind(on_keyboard=self.hook_keyboard)

def hook_keyboard(self, window, key, *largs):
    if key == 27:
       # do what you want, return True for stopping the propagation
       return True 

i guess that i have solved it but should thank both @inclement and @qua-non! your answers guys led me to the right way! so in kv i assume that i gave an id to my screen manager (please refer to my question where i have written the kv code) , in python i should do the following:

    from kivy.core.window import Window
    from kivy.properties import ObjectProperty

    class MyAppClass(FloatLayout):#its a FloatLayout in my case
        _screen_manager=ObjectProperty(None)
        def __init__(self,**kwargs):
            super(MyAppClass,self).__init__(**kwargs)
            #code goes here and add:
            Window.bind(on_keyboard=self.Android_back_click)

        def Android_back_click(self,window,key,*largs):
            if key == 27:
                self._scree_manager.current='screen1'#you can create a method here to cache in a list the number of screens and then pop the last visited screen.
                return True

    class MyApp(App):
        def build(self):
            return MyAppClass()

    if __name__=='__main__':
        MyApp().run()