How i can change it before i create it

I need to load posts when I go to NewsScreen before it has loaded. When I put posts_show() method to init(), it says that "AttributeError: 'NoneType' object has no attribute 'text' cuz it hadn't created yet. What am I doing wrong? If you know please tell me, I'd really appreciate it

Here is my py file:

class NewsScreen(Screen):
    SCREEN_NAME = meta.SCREENS.NEWS_SCREEN
    dialog_post = None
    dialog_plus = None
    post = ObjectProperty()
    md = ObjectProperty()

    def __init__(self, **kw):
        super().__init__(name=self.SCREEN_NAME, **kw)
        self.response = news_request()
        print(self.response.json())
        #text=username.json()['username'], tertiary_text=content.json()
        self.posts_show()
    def post_change(self, post_text, post_content):
        self.post.text = post_text
        self.post.tertiary_text = post_content
    def build(self):
        return Builder.load_string(KV)

    def posts_show(self):
        for post in self.response.json().values():
            post_text = post['username']
            post_content = post['content']
            self.post_change(post_text, post_content)
    ```
Here is kivy:
```py
        ScrollView:
            MDList:
                id: md
                ThreeLineAvatarIconListItem:
                    id: post
                    on_press: root.post_show()
                    text: "username"
                    secondary_text: "data"
                    tertiary_text: f"[color=#000000][font=Roboto]Post_text[/font] [/font][/color]"
                    IconLeftWidget:
                        icon: "language-python"