Estoy haciendo una aplicación. Hasta donde sé, estoy haciendo las cosas correctamente pero todavía obtengo este error.

word = self.search_box.text AttributeError: el objeto 'NoneType' no tiene el atributo 'text'

He comprobado los errores tipográficos y otros errores comunes que todavía no funcionan.

aquí está el código

import kivy
kivy.require('1.10.0')

from kivy.uix.stacklayout import StackLayout
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label 
from kivy.app import App
from kivy.uix.popup import Popup  
from kivy.uix.screenmanager import ScreenManager, Screen 
from kivy.lang import Builder 
from kivy.properties import ObjectProperty
from kivy.uix.textinput import TextInput
from kivy.properties import StringProperty


import json

Builder.load_file('VocabularyJournal.kv')

class MenuPage(Screen):
    pass

class DisplayPage(Screen):
    search_box= ObjectProperty()
    label_maening=StringProperty()
    label_synonym=StringProperty()
    label_ant=StringProperty()
    label_sentence=StringProperty()


    def __init__(self, **kwargs):
        super(DisplayPage,self).__init__(**kwargs)
        with open('vocab_words.json') as rfile:
            data=json.load(rfile)

        word=self.search_box.text               #the error occurred here 

        for value in data:
            if value['word']==word:
                self.label_maening=value['meaning']
                self.label_synonym=value['synonym']
                self.label_ant=value['antonyms']
                self.label_sentence=value['sentence']


class WordInsertPage(Screen):
    pass


class NewWordPage(Screen):
    word_box = ObjectProperty()
    meaning_box = ObjectProperty()
    synonym_box = ObjectProperty()
    ant_box = ObjectProperty()
    sentence_box = ObjectProperty()


    def saving_data(self):

        with open('vocab_words.json') as rfile:
            data=json.load(rfile)


        entry={'word': self.word_box.text, 'meaning': self.meaning_box.text, 'synonym': self.synonym_box.text, 'antonyms': self.ant_box.text, 'sentence': self.sentence_box.text}
        data.append(entry)


        with open('vocab_words.json','w') as wfile:
            json.dump(data,wfile,indent=4)


class FlashCard(Screen):
    pass

class WordGroups(Screen):
    pass

class Manager(ScreenManager):
    pass

class VocabularyJournalApp(App):
    def build(self):
        return Manager()

object = VocabularyJournalApp()
object.run()

aquí está el código kv

<Manager>:
    MenuPage:
        name: 'menu'
    WordInsertPage:
        name: 'insertword'
    NewWordPage:
        name: 'newword'
    FlashCard:
        name: 'flashcard'
    WordGroups:
        name: 'wordgroup'
    DisplayPage:
        name: 'display'

<MenuPage>:
    Label: 
        text: "Vocabulary Journal"
        size_hint: .90,.10

    StackLayout:
        orientation: 'tb-rl'
        spacing: 10
        padding: 10

        Button:
            text: 'Search'
            size_hint: None,.20
            width: 130
            background_down:'darkgrey.png'
            on_press: root.manager.current='insertword'
        Button:
            text: 'New Word'
            size_hint: None,.20
            width: 130
            background_down:'darkgrey.png'
            on_press: root.manager.current='insertword'
        Button:
            text: 'Flash Cards'
            size_hint: None,.20
            width: 130
            background_down:'darkgrey.png'
            on_press: root.manager.current='flashcard'

        Button:
            text: 'Word Groups'
            size_hint: None,.20
            width: 130
            background_down:'darkgrey.png'
            on_press: root.manager.current='wordgroup'

<WordInsertPage>:

    FloatLayout:

        Button: 
            text: "New Word"
            on_press: root.manager.current='newword'
            font_size: 30
            color: 0,0,0,1
            size_hint: .2, .1
            pos_hint: {"center_x": .5, "center_y": 0.3}
            background_down: 'darkgrey.png'
        Button:
            text: "search word"
            on_press: root.manager.current='display'
            font_size: 30
            color: 0,0,0,1
            size_hint: .2, .1
            pos_hint: {"center_x": .5, "center_y": 0.5}
            background_down: 'darkgrey.png'
        Button:
            text: 'Flash Cards'
            on_press: root.manager.current="flashcard"
            font_size: 30
            color: 0,0,0,1
            size_hint: .2, .1
            pos_hint: {"center_x": .5, "center_y": 0.7}
            background_down: 'darkgrey.png'



<NewWordPage>:
    id: refer_to_it
    word_box: word_input
    meaning_box: meaning_input
    synonym_box: Synonym_input
    ant_box: ant_input
    sentence_box: sentence_input
    StackLayout:
        orientation: 'tb-rl'
        spacing: 10
        padding: 90
        TextInput:
            text: "write your word here"
            color: 1,1,1,1
            id: word_input
            width: 300
            size_hint: None, .10

        TextInput:
            text: "write meaning of your word here"
            color: 1,1,1,1
            id: meaning_input
            width: 600
            size_hint: None, .20

        TextInput:
            text: "write Synonyms of your word here"
            color: 1,1,1,1
            id: Synonym_input
            width: 600
            size_hint: None, .20

        TextInput:
            text: "write antonyms of your text here"
            color: 1,1,1,1
            id: ant_input
            width: 600
            size_hint: None, .20

        TextInput:
            text: "write a sentence based on your word here"
            color: 1,1,1,1
            id: sentence_input
            width: 600
            size_hint: None, .20

        Button:
            text: 'Save'
            size_hint: None,.10
            width: 130
            background_down:'darkgrey.png'
            on_press: refer_to_it.saving_data()     

<DisplayPage>:
    search_box: search_text  # search_box is the reference to the textinput in py file
    BoxLayout:
        size_hint_y: None
        height: '48dp'

        TextInput:
            text:'enter the word you wanna search here'
            id: search_text


        ToggleButton:
            id: tog
            text: 'Horizontal'
            group: 'accordion'
            state: 'down'

        ToggleButton:
            text: 'Vertical'
            group: 'accordion'

    Accordion:
        orientation: 'horizontal' if tog.state == 'down' else 'vertical'    

        AccordionItem:
            title:'meaning'

            Label:
                text: root.label_maening
                text_size: self.width, None

        AccordionItem:
            title:'Synonym'

            Label:
                text: root.label_synonym
                text_size: self.width, None

        AccordionItem:
            title:'Antonym'

            Label:
                text: root.label_ant
                text_size: self.width, None

        AccordionItem:
            title:'Sentence'

            Label:
                text: root.label_sentence
                text_size: self.width, None