title: Invalid property name in a simple example
body: <p>I've copied this code from a book about Kivy and python</p>
  
  <p><strong>main.py</strong></p>
  
  <pre><code>from kivy.app import App
  from kivy.uix.boxlayout import BoxLayout
  from kivy.properties import ObjectProperty
  from kivy.network.urlrequest import UrlRequest
  
  import json
  
  class AddLocationForm(BoxLayout):
      search_input = ObjectProperty()
      search_results = ObjectProperty()
  
      def search_location(self) :
          search_template = "http://api.openweathermap.org/data/2.5/find?q={}&amp;type=like"
          search_url = search_template.format(self.search_input.text)
          request = UrlRequest(search_url, self.found_location)
  
      def found_location(self, request, data) :
          data = json.loads(data.decode())
          cities = [ "{} ({})".format(d['name'], d['sys']['country']) for d in data['list'] ]
          self.search_results.item_strings = cities
  
  class WeatherApp(App):
      pass
  
  
  if __name__ == "__main__" :
      WeatherApp().run()
  </code></pre>
  
  <p><strong>weather.kv</strong></p>
  
  <pre><code>AddLocationForm:
  
  &lt;AddLocationForm&gt;:
      orientation: "vertical"
      search_input: search_box
      search_results: search_results_list
      BoxLayout:
          height: "40dp"
          size_hint_y: None
          TextInput: 
              id: search_box
              size_hint_x: 50
          Button:
              text: "Search"
              size_hint_x: 25
              on_press: root.search_location()
          Button:
              text: "Current location"
              size_hint_x: 25
      ListView:
          id : search_results_list
          item_strings: []
  </code></pre>
  
  <p>Why do I get the following error?  </p>
  
  <pre><code>Traceback (most recent call last):
   File "main.py", line 27, in &lt;module&gt;
     WeatherApp().run()
   File "C:\Kivy\kivy\kivy\app.py", line 765, in run
     self.load_kv(filename=self.kv_file)
   File "C:\Kivy\kivy\kivy\app.py", line 585, in load_kv
     root = Builder.load_file(rfilename)
   File "C:\Kivy\kivy\kivy\lang.py", line 1444, in load_file
     return self.load_string(data, **kwargs)
   File "C:\Kivy\kivy\kivy\lang.py", line 1491, in load_string
     parser = Parser(content=string, filename=fn)
   File "C:\Kivy\kivy\kivy\lang.py", line 1049, in __init__
     self.parse(content)
   File "C:\Kivy\kivy\kivy\lang.py", line 1122, in parse
     objects, remaining_lines = self.parse_level(0, lines)
   File "C:\Kivy\kivy\kivy\lang.py", line 1218, in parse_level
     level + 1, lines[i:], spaces)
   File "C:\Kivy\kivy\kivy\lang.py", line 1228, in parse_level
     'Invalid property name')
  kivy.lang.ParserException: Parser: File ".\weather.kv", line 21:
  ...
      19:                       size_hint_x: 25
      20:       ListView:
  &gt;&gt;   21:               id : search_results_list
      22:               item_strings: []
  ...
  Invalid property name
  </code></pre>