Kivy, TypeError: 'NoneType' object has no attribute '__getitem__'

Question

While trying to run a sample kivy application, i m facing the above error.

here is the python code:

main.py.

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.screenmanager import Screen, ScreenManager, FadeTransition

class MyScreenManager(ScreenManager):
    pass

class MainScreen(Screen):
    pass

class MailScreen(Screen):
    pass

class ProjectScreen(Screen):
    pass

class IntroScreen(Screen):
    pass

class GsaMain(BoxLayout):
    pass

class GsamApp(App):
    def build(self):
        return MyScreenManager()

GsamApp().run()

the kivy file named gsam.kv

MyScreenManager:
    IntroScreen:
    MainScreen:
    PrjcScreen:
    MailScreen:
    ChatScreen:

<IntroScreen>:
    name: 'introscreen'
    BoxLayout:
        Label:
            text: 'Welcome to GSAM'
            font_size: 35
    BoxLayout:
        Label:
            text: "Login"
        TextInput:
            id: login
            text: "Login"
        Button:
            text: "Connect"
            on_release: root.current = 'mainpage'
    BoxLayout:
        Button:
            text: 'Project Page'
            font_size: 25
            on_release: app.root.current = 'main'

<MainScreen>:
    name: 'main'
    BoxLayout:
        Label:
            text: 'Your GSAM Portal'
            font_size: 35
    BoxLayout:
        Button:
            text: 'Check Mails'
            font_size: 25
            on_release: app.root.current = 'mailscreen'
            canvas:
            color: rgba: 1,0,0,1
                Rectangle:
                    size: 50, 50
                    Label: "Post Projects"
                    id: projct
                Rectangle:
                    size: 50, 50
                    Label: "Messages"
                    id: msgs

<MailScreen>:
    name: 'mailscreen'
    BoxLayout:
        Label:
            text: 'GSAM Mail'
            font_size: 35
    BoxLayout:
        Button:
            text: 'Chat'
            font_size: 25
            on_release: app.root.current = 'chat'
<ChatScreen>:
    name: 'chatscreen'
    BoxLayout:
        Label:
            text: 'Chat with your Colleagues'
            font_size: 35
    BoxLayout:
        Button:
            text: 'Home'
            font_size: 25
            on_release: app.root.current = 'main'

<PrjcScreen>:
    name: 'prjcscreen'
    BoxLayout:
        Label:
            text: 'Community Projects'
            font_size: 35
    BoxLayout:
        Button:
            text: 'community Projects'
            font_size: 25
            on_release: app.root.current = 'main'
            GridLayout:
                cols: 2
                rows: 4
                padding: 5
                spacing: 5
                    Label:
                        text: "Project Title"
                    TextInput:
                        id: ptitle
                    Label:
                        text: "Project Description"
                    TextInput:
                        id: pdescr

I can't figure out what is the traceback pointing to.

 Traceback (most recent call last):
   File "main.py", line 28, in <module>
     GsamApp().run()
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/app.py", line 797, in run
     self.load_kv(filename=self.kv_file)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/app.py", line 594, in load_kv
     root = Builder.load_file(rfilename)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1749, in load_file
     return self.load_string(data, **kwargs)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1796, in load_string
     parser = Parser(content=string, filename=fn)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1185, in __init__
     self.parse(content)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1287, in parse
     objects, remaining_lines = self.parse_level(0, lines)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1384, in parse_level
     level + 1, lines[i:], spaces)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1384, in parse_level
     level + 1, lines[i:], spaces)
   File "/home/afidegnum/gsam/local/lib/python2.7/site-packages/kivy/lang.py", line 1437, in parse_level
     if current_property[:3] == 'on_':
 TypeError: 'NoneType' object has no attribute '__getitem__'

do I need to define a function on_release in python code?

Answer 1

I have worked on your code and produce a working one. Aside the suggestions given above, I have also noticed in your .kv file, there were lots of indentation problems. I gave comments wherever necessary I made those changes. Find the working code below:

main.py

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout   
from kivy.uix.screenmanager import Screen, ScreenManager, FadeTransition

class MyScreenManager(ScreenManager):
    pass

class MainScreen(Screen):
    pass

class MailScreen(Screen):
    pass

class ChatScreen(Screen):
    pass

class ProjectScreen(Screen):
    pass

class IntroScreen(Screen):
    pass

class GsaMain(BoxLayout):
    pass

class GsamApp(App):
    def build(self):
        sm = MyScreenManager()
        sm.add_widget(IntroScreen(name="introscreen"))
        sm.add_widget(MainScreen(name="main"))
        sm.add_widget(MailScreen(name="mailscreen"))
        sm.add_widget(ProjectScreen(name="prjcscreen"))
        sm.add_widget(ChatScreen(name='chat'))
        return sm

GsamApp().run()

gsma.kv

<IntroScreen>:
    name: 'introscreen'
    BoxLayout:
        orientation: 'vertical'
        padding: 100,100
        spacing: 50
        Label:
            text: 'Welcome to GSAM'
            font_size: 35
        Label:
            text: "Login"
        TextInput:
            id: login
            text: "Login"

   # BoxLayout:     # this makes the button widget covers the whole page. remove it
        Button:
            text: "Connect"
            on_release: app.root.current = 'main'
        Button:
            text: 'Project Page'
            font_size: 15
            on_release: app.root.current = 'prjcscreen'

<MainScreen>:
    name: 'main'
    BoxLayout:
        orientation:'vertical'
        padding:100,100
        spacing:50
        Label:
            text: 'Your GSAM Portal'
            font_size: 35
        # BoxLayout: # remove this. Dont repeat BoxLayout for every widget u want show on the screen except for a good reason. Or better still, ident the BoxLayout as a child of the First Boxlayout
        Button:
            text: 'Check Mails'   # text, font_size,on_realease must not  be in the same line with button
            font_size: 25
            on_release: app.root.current = 'mailscreen'

            canvas.before:
                Color:              # I have reidented Color
                     rgba: 1,0,0,1   # this line must be here
                Rectangle:          # Rectangle must ident with Color
                    size: 50, 50
                    # Label: "Post Projects"     # remove the label here
                    id: projct                   # and place it either before of after canvas class
                Rectangle:
                    size: 50, 50
                    # Label: "Messages"
                    id: msgs

<MailScreen>:
    name: 'mailscreen'
    BoxLayout:
        Label:
            text: 'GSAM Mail'
            font_size: 35
        Button:
            text: 'Chat'
            font_size: 25
            on_release: app.root.current = 'chat'

 <ChatScreen>:
    name: 'chatscreen'
    BoxLayout:
        Label:
            text: 'Chat with \nyour Colleagues'
            font_size: 35
        Button:
            text: 'Home'
            font_size: 25
            on_release: app.root.current = 'main'

<ProjectScreen>:
    name: 'prjcscreen'
    BoxLayout:
        Label:
            text: 'Community Projects'
            font_size: 35

        Button:
            text: 'community Projects'
            font_size: 25
            on_release: app.root.current = 'main'
            GridLayout:
                cols: 2
                rows: 4
                padding: 5
                spacing: 5
                Label:
                    text: "Project Title"
                TextInput:
                    id: ptitle
                Label:
                    text: "Project Description"
                TextInput:
                    id: pdescr

Answer 2

main.py

• There's no ChatScreen. Define one:

  class ChatScreen(Screen):
      pass
  

• ProjectScreen should be renamed to PrjcScreen to match the name in gsam.kv. (Or Change PrjcScreen in gsam.kv)

gsam.kv

• color -> Color:

  color: rgba: 1,0,0,1
  

  ->

  Color:
      rgba: 1,0,0,1
  

• Rectangle does not have Label parameters:

          Rectangle:
              size: 50, 50
              # Label: "Post Projects"  <---
              id: projct
          Rectangle:
              size: 50, 50
              # Label: "Messages"  <---
              id: msgs