python - Linking main.py with .kv file -

i trying label has text of string stored in w variable in main.py file , label in .kv file let me show both files.

here's main.py file

from kivy.app import app kivy.properties import stringproperty  class exampleapp(app):       def hell(self):         w="hello world"     def build(self):         self.load_kv("exapmleapp.kv")  if __name__ == "__main__":     exampleapp().run() 

and here .kv file.

label:     text:app.w 

every time when run main.py file, gives me error.

1: 2:label: 3: text:app.w ... attributeerror: 'exampleapp' object has no attribute 'w' file "/usr/local/lib/python2.7/dist-packages/kivy/lang.py", line 1649, in create_handler return eval(value, idmap) file "./exampleapp.kv", line 3, in text:app.w file "/usr/local/lib/python2.7/dist-packages/kivy/lang.py", line 858, in getattribute return getattr(object.getattribute(self, '_obj'), name) file "/usr/local/lib/python2.7/dist-packages/kivy/lang.py", line 2011, in _apply_rule value, rule, rctx['ids']) file "/usr/local/lib/python2.7/dist-packages/kivy/lang.py", line 1654, in create_handler cause=tb)

how can label has text stored in w variable in main.py file

i don't think .kv file can see attributes inside function calling. can see in example below, i've moved 'w' attribute outside function.

edit: aah seems want change displayed label when function hell() called. firstly need easy way refer label. kivy uses id tag, , list of ids can found in self.ids

having 'w' variable no longer necessary, i've left in there answer original question.

so, should work in theory:

from kivy.app import app kivy.properties import stringproperty  class exampleapp(app):     w = "hello"   def hell(self):     self.ids.mylabel.text = "world"   def build(self):     self.load_kv("exapmleapp.kv")  if __name__ == "__main__":   exampleapp().run() 

and .kv file:

label:   id: mylabel   text:app.w