[Python] How to link kivy code (that isn't in a kivy file, but is in the python code) to...

I'm codding a simple app. Right now, I made a log in page. But the buttons seems to not be working. The issues is that the buttons are not "linked" to the python class. And so, they don't have acess to the functions that describe their behavior.

When it was a .kv file, this issues didn't happen. I know I could just stranfer it back into a kivy file. But I am still knew at kivy, and I want to learn (and not find an easy way out).

Here is my code.

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder
from kivymd.app import MDApp
import pymongo
from kivy.properties import StringProperty
import hashlib
from pymongo.errors import ConnectionFailure, DuplicateKeyError
from kivy.uix.widget import Widget

screen_helper = """

ScreenManager:
MenuScreen:
LoginScreen:
SignupScreen:

<MenuScreen>:
name: 'menu'
MDRectangleFlatButton:
text: 'Sign up'
pos_hint: {'center_x':0.5,'center_y':0.6}
on_press: root.manager.current = 'Sign up page'
MDRectangleFlatButton:
text: 'log in'
pos_hint: {'center_x':0.5,'center_y':0.5}
on_press: root.manager.current = 'Log in page'

<SignupScreen>:
name: 'Sign up page'
MDLabel:
text: 'Sign up here'
halign: 'center'
MDRectangleFlatButton:
text: 'Back'
pos_hint: {'center_x':0.5,'center_y':0.1}
on_press: root.manager.current = 'menu'

<LoginScreen>:
name: 'Log in page'
Screen:
MDCard:
size_hint: None, None
size: 500,600
pos_hint: { "center_x": 0.5, "center_y": 0.5}
elevation: 10
padding:25
spacing:25
orientation: 'vertical'

MDLabel:
id: welcome_label
text: "Welcome"
font_size: 40
halign: 'center'
size_hint_y: None
height: self.texture_size[1]
padding_y: 15

MDTextField:
id: name
hint_text: "write your name"
icon_right: "account"
size_hint_x: None
width: 300
font_size: 20
pos_hint:{'center_x': 0.5}
line_color_normal: (0, 0, 0, 1) # Change line color if you want it
line_color_focus: (0, 0, 0, 1) # Line color when focused
multiline: False

MDTextField:
id: number
hint_text: "e.g: +243 123 209 977"
icon_right: "numeric"
size_hint_x: None
width: 300
font_size: 20
pos_hint:{'center_x': 0.5}
line_color_normal: (0, 0, 0, 1) # Change line color if you want it
line_color_focus: (0, 0, 0, 1) # Line color when focused
multiline: False

MDTextField:
id: password
hint_text: "write your password"
icon_right: "eye-off"
size_hint_x: None
width: 300
font_size: 20
pos_hint:{'center_x': 0.5}
line_color_normal: (0, 0, 0, 1) # Change line color if you want it
line_color_focus: (0, 0, 0, 1) # Line color when focused
multiline: False
password:True

MDRoundFlatButton:
text: "log in"
font_size: 20
pos_hint:{"center_x": 0.5}
on_press: LogingScreen.login()
MDRoundFlatButton:
text: "reset"
font_size: 20
pos_hint:{"center_x": 0.5}
on_press: LoginScreen.reseting_login()

"""


class MenuScreen(Screen):
pass


class LoginScreen(Screen):
def build(self):
self.theme_cls.theme_style = "Dark"
self.theme_cls.primary_palette = 'BlueGray'
try:
self.client = pymongo.MongoClient(
"mongodb+srv://gyanyoni25:yonigyan@patnouv.hhopv.mongodb.net/?retryWrites=true&w=majority&appName=PatNouv" # Correct format
)
self.db = self.client["Users"] # Replace with your DB name
self.collection = self.db["Clients"] # Replace with your collection name
# Test connection (optional)
self.client.admin.command('ping')
print("Successfully connected to MongoDB Atlas!")
except ConnectionFailure as e:
print(f"Connection failed during startup: {e}")
self.root.ids.welcome_label.text = "Database Connection Error" # Show error in UI
return # Prevent app from loading if connection fails
except Exception as e:
print(f"An unexpected error occurred during startup: {e}")
self.root.ids.welcome_label.text = "Database Connection Error" # Show error in UI
return

return Builder.load_file('loginpage.kv')

def login(self):
name_data = self.root.ids.name.text
number_data = self.root.ids.number.text
password_data = self.root.ids.password.text

if name_data and number_data and password_data:
try:
hashed_password = hashlib.sha256(password_data.encode()).hexdigest()

user_data = {
"name": name_data,
"number": number_data,
"password": hashed_password
}

self.collection.insert_one(user_data)
print("Login Successful")
self.root.ids.welcome_label.text = f"Hey, {name_data}"
self.reseting_login()

except ConnectionFailure as e:
print(f"Connection error during login: {e}")
self.root.ids.welcome_label.text = "Connection Error"
except DuplicateKeyError as e:
print(f"Duplicate key error: {e}")
self.root.ids.welcome_label.text = "Username/Number already exists"
except Exception as e:
print(f"An error occurred during login: {e}")
self.root.ids.welcome_label.text = "An error occurred"

else:
print("Please fill in all fields.")
self.root.ids.welcome_label.text = "Please fill in all fields"

def reseting_login(self):
self.root.ids.name.text = ""
self.root.ids.number.text = ""
self.root.ids.password.text = ""
self.root.ids.welcome_label.text = "Welcome" # Reset welcome message



class SignupScreen(Screen):
pass


# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(LoginScreen(name='Login'))
sm.add_widget(SignupScreen(name='SignUp'))


class egy (MDApp):

def build(self):
screen = Builder.load_string(screen_helper)
return screen


What I tried:

1. At first it was app.reseting_login(). So I changed app to LoginScreen (name of my function).
2. I made sure that the screen in the kivy code and the class had the same name
3. Changing into a .kv file (worked, but I don't want to take the easy way out).

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