title: Kivy ScreenManager Errors
body: <p>I'm a beginner with kivy language. I'm writing an app but I have some difficulties. My app is going to consist of a few screens so I decided to use the ScreenManager but each time I'm trying to launch the .py I get an error and this makes the python not responding. I have saved both the .py file and the .kv file in the same folder.</p>
  
  <pre><code>Traceback (most recent call last):
     File "C:\Users\Eng. Aladdin Hammodi\Desktop\kivy\main.py", line 15, in &lt;module&gt;
       presentation = Builder.load_file(Aladdin.kv)
   NameError: name 'Aladdin' is not defined
  </code></pre>
  
  <p>Python file:
  </p>
  
  <pre><code>import kivy
  kivy.require("1.9.1")
  
  from kivy.app import App
  from kivy.uix.widget import Widget
  from kivy.uix.screenmanager import ScreenManager, Screen
  from kivy.uix.floatlayout import FloatLayout
  from kivy.uix.popup import Popup
  from kivy.core.window import Window
  from kivy.uix.textinput import TextInput
  from kivy.properties import ObjectProperty
  from kivy.uix.button import Button
  from kivy.lang import Builder
  
  presentation = Builder.load_file(Aladdin.kv)
  
  
  class ScreenOne(Screen):
      pass
  
  
  class ScreenTwo(Screen):
      pass
  
  class ScreenManager(ScreenManager):
      pass
  
  
  class AladdinApp(App):
      def build(self):
          return presentation
  
  sample_app = AladdinApp()
  sample_app.run()
  </code></pre>
  
  <p>aladdin.kv</p>
  
  <pre><code>&lt;ScreenOne&gt;:
      name:screen1
  
      FloatLayout:
          canvas:
              source:'image1'
          Label:
              text:'Hello\n Welcome to my app\n'
              font_size: 40
  
          Button:
              text: 'Next'
              pos: 0,1
              font_size:20
              hint_size:0.1,0.05
              on_press:root.manager.current='screen2'
  &lt;ScreenTwo&gt;:
      name:screen2
      FloatLayout:
         canvas:
              source:'image1'
          Label:
              text:'Please insert your name'
              text:'Please insert your Password'
              font_size: 40
  
          Button:
              text: 'Next'
              pos: 0,1
              font_size:20
              hint_size:0.1,0.05
              on_press:root.manager.current='screen1'
  </code></pre>