Kivy returns blank black screen?

Question

So I was following this guy's video on Kivy Tutorial, and I'm extremely new to python and the kivy stuff. But when I copy the exact same line of codes:

main kivy.py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder

Builder.load_file("thelab.kv")

class MainWidget(Widget):
    pass
class thelabApp(App):
    pass

thelabApp().run()

thelab.kv

MainWidget:

<MainWidget>:
    Button:
        text: 'Hello'
        size: "400dp", "200dp"
        pos: "100dp", "200dp"

all that shows up is a black screen. There's seems to be no problem with the installation of kivy. And no error messages. What do I do?

Answer 1

Okay! So, I solved it. I put the .kv file in a different folder, and when I move it to the same one, it seems to work. I (also) might have forgotten to save the .kv file?