Can't use transitions in kv lang
<p>App code:</p>

<pre><code>from kivy.app import App
from kivy.lang import Builder
from kivy.factory import Factory
from kivy.uix.screenmanager import Screen
from kivy.uix.screenmanager import ScreenManager
from kivy.uix.screenmanager import FadeTransition&lt;br/&gt;
kv = '''
ScreenManagement:
    transition: FadeTransition()
    screen1:
    screen2:
&lt;screen1&gt;:
    name: 'one'
    Button:
        text: 'Hello!'
        on_release: app.root.current = 'two'
&lt;screen2&gt;:
    name: 'two'
    Button:
        text: 'Hello2'
        on_release: app.root.current = 'one'
'''&lt;br/&gt;
class screen1(Screen):
    pass
class screen2(Screen):
    pass
class ScreenManagement(ScreenManager):
    pass
class test23(App):
    def build(self):
        return Builder.load_string(kv)
        &lt;br/&gt;
if __name__ == '__main__':
    test23().run()
</code></pre>

<p>Every time I execute it I have the following traceback. What's wrong with it?</p>

<pre><code> runfile('/home/pc/python and kivy/test23.py', wdir='/home/pc/python and kivy')&lt;br/&gt;
 Traceback (most recent call last):&lt;br/&gt;
   File "&lt;stdin&gt;", line 1, in &lt;module&gt;&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell/sitecustomize.py", line 699, in runfile&lt;br/&gt;
     execfile(filename, namespace)&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell/sitecustomize.py", line 81, in execfile&lt;br/&gt;
     builtins.execfile(filename, *where)&lt;br/&gt;
   File "/home/pc/python and kivy/test23.py", line 42, in &lt;module&gt;&lt;br/&gt;
     test23().run()&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 802, in run
     root = self.build()&lt;br/&gt;
   File "/home/pc/python and kivy/test23.py", line 39, in build
     return Builder.load_string(kv)&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1921, in load_string&lt;br/&gt;
     self._apply_rule(widget, parser.root, parser.root)&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 2130, in _apply_rule
     e), cause=tb)&lt;br/&gt;
 kivy.lang.BuilderException: Parser: File "&lt;inline&gt;", line 3:
 ..&lt;br/&gt;
       1:&lt;br/&gt;
       2:ScreenManagement:&lt;br/&gt;
 &gt;&gt;    3:    transition: FadeTransition()&lt;br/&gt;
       4:    screen1:&lt;br/&gt;
       5:    screen2:&lt;br/&gt;
 ..&lt;br/&gt;
 BuilderException: Parser: File "&lt;inline&gt;", line 3:
 ..&lt;br/&gt;
       1:&lt;br/&gt;
       2:ScreenManagement:&lt;br/&gt;
 &gt;&gt;    3:    transition: FadeTransition()&lt;br/&gt;
       4:    screen1:&lt;br/&gt;
       5:    screen2:&lt;br/&gt;
 ..&lt;br/&gt;
 NameError: name 'FadeTransition' is not defined&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1742, in create_handler&lt;br/&gt;
     return eval(value, idmap), bound_list&lt;br/&gt;
   File "&lt;string&gt;", line 3, in &lt;module&gt;&lt;br/&gt;&lt;br/&gt;

   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 2115, in _apply_rule
     rctx['ids'])&lt;br/&gt;
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1747, in create_handler
     cause=tb)&lt;br/&gt;
</code></pre>