python - Nested / alternating apps with Kivy -

i'd have kivy app function launcher other kivy apps, depending on input. way implemented below not working (because kv file gets reloaded , styles reapplied, adding more , more buttons), , there seems recursion trace suggests when hit esc exit.

i warning app1.kv loaded multiple times, however, in documentation app.load_kv() says

this method invoked first time app being run if no widget tree has been constructed before app.

this implies me should possible run() app multiple times?

here code:

main.py

from kivy.uix.widget import widget kivy.uix.gridlayout import gridlayout kivy.app import app kivy.properties import objectproperty kivy.uix.button import button kivy.clock import clock kivy.logger import logger kivy.lang import builder  class outsideapp(app):     current_app = objectproperty(none)      def build(self):         clock.schedule_interval(self.update, 3)         return widget()      def update(self, dt):         if isinstance(self.current_app, app):             self.current_app.stop()         if isinstance(self.current_app, app1):             self.current_app = app2()         else:             self.current_app = app1()         self.current_app.run()  class app1(app):     pass class app2(app):     def build(self):         gl = builder.load_string("<sequencesgame@gridlayout>:\n cols: 2\n   button:\n       text: \"hello 2\"\nsequencesgame:")         return gl  if __name__ == '__main__':     oa = outsideapp()     oa.run() 

app1.kv

#:kivy 1.0.9 <sequencesgame@gridlayout>:     cols: 2     button:         text: "hello 111" sequencesgame: 

this seems issue if apps not nested:

main2.py

from kivy.app import app  kivy.clock import clock kivy.logger import logger kivy.lang import builder  class app1(app):     pass class app2(app):     def build(self):         return builder.load_string("<sequencesgame@gridlayout>:\n   cols: 2\n   button:\n       text: \"hello 2\"\nsequencesgame:")  current_app = none  def switch(*args):     global current_app     if isinstance(current_app, app):         current_app.stop()     if isinstance(current_app, app1):         current_app = app2()     else:         current_app = app1()     current_app.run()  if __name__ == '__main__':     clock.schedule_interval(switch, 2)     switch() 

in end followed @inclement's suggestion of using multiprocessing. here basic implementation (without communication through pipes or queues):

import sys import multiprocessing kivy.app import app kivy.lang import  builder time import sleep#, localtime, time  def str_to_class(str):     return reduce(getattr, str.split("."), sys.modules[__name__])  class app1(app):     def build(self):         return builder.load_string("boxlayout:\n    button:\n       text: \"hello 1\"")  class app2(app):     def build(self):         return builder.load_string("boxlayout:\n    button:\n       text: \"hello 2\"")   class wrapper(object):     def __init__(self, *kargs, **kwargs):         super(wrapper, self).__init__()         self.running_app = none         self.next_app = 'app1'      def change_running_app(self, name='app1'):         if self.running_app not none:             self.running_app.terminate()         self.running_app = multiprocessing.process(target=self.run_app, kwargs={'name':name})         self.running_app.start()      def run_app(self, name='app1'):         app = str_to_class(name)()         app.run()      def swap(self):         self.change_running_app(name=self.next_app)         self.next_app = ['app1', 'app2']['app1' self.next_app]  if __name__ == '__main__':     counter = 0     w = wrapper()     while true:         counter += 1         print "started app instance {}".format(counter)         w.swap()         sleep(5)