Eu estou seguindotutoriais para Kivy e não consegui carregar corretamente as propriedades dos arquivos .kv. Por alguma razão, às vezes consigo extrair arquivos .kv por meio de umfor kv in listdir(kv_path): Builder.load_file(kv_path+kv), mas não posso fazê-lo simplesmente colocando os arquivos kv no mesmo diretório raiz e deixando "importar por si só?"

Como exemplo, ao usar os arquivos:
main.py

from kivy.app import App  
from kivy.uix.label import Label   
from kivy.uix.widget import Widget  

class Widgets(Widget):
    pass
class SimpleKivy3(App):
    def build(self):
        return Widgets()

if __name__ == "__main__":
    SimpleKivy3().run()

SimpleKivy3.kv

<Button>:
    font_size: 40
    size: 170,75
    color: 0,1,0,1

<Widgets>:
    Button:
        pos: root.x, root.top - self.height
        text: "Kivy"

    Button:
        pos: 170,0
        text: "Tutorials"

Eu obtenho a seguinte saída no meu terminal:

$ python main.py 
[INFO   ] [Logger      ] Record log in /home/nickshu/.kivy/logs/kivy_18-09-12_58.txt
[INFO   ] [Kivy        ] v1.11.0.dev0, git-038acbf, 20180912
[INFO   ] [Python      ] v3.6.5 |Anaconda, Inc.| (default, Apr 29 2018, 16:14:56) 
[GCC 7.2.0]
[INFO   ] [Factory     ] 195 symbols loaded
[INFO   ] [Image       ] Providers: img_tex, img_dds, img_sdl2, img_pil, img_gif (img_ffpyplayer ignored)
[INFO   ] [Text        ] Provider: sdl2
[INFO   ] [Window      ] Provider: sdl2(['window_egl_rpi'] ignored)
[INFO   ] [GL          ] Using the "OpenGL" graphics system
[INFO   ] [GL          ] Backend used <gl>
[INFO   ] [GL          ] OpenGL version <b'3.0 Mesa 18.0.5'>
[INFO   ] [GL          ] OpenGL vendor <b'Intel Open Source Technology Center'>
[INFO   ] [GL          ] OpenGL renderer <b'Mesa DRI Intel(R) HD Graphics P630 (Kaby Lake GT2) '>
[INFO   ] [GL          ] OpenGL parsed version: 3, 0
[INFO   ] [GL          ] Shading version <b'1.30'>
[INFO   ] [GL          ] Texture max size <16384>
[INFO   ] [GL          ] Texture max units <32>
[INFO   ] [Window      ] auto add sdl2 input provider
[INFO   ] [Window      ] virtual keyboard not allowed, single mode, not docked
[INFO   ] [ProbeSysfs  ] device match: /dev/input/event6
[INFO   ] [MTD         ] Read event from </dev/input/event6>
[INFO   ] [Base        ] Start application main loop
[INFO   ] [MTD         ] </dev/input/event6> range position X is 1266 - 5676
[INFO   ] [MTD         ] </dev/input/event6> range position Y is 1094 - 4762
[INFO   ] [MTD         ] </dev/input/event6> range touch major is 0 - 0
[INFO   ] [MTD         ] </dev/input/event6> range touch minor is 0 - 0
[INFO   ] [MTD         ] </dev/input/event6> range pressure is 0 - 255
[INFO   ] [MTD         ] </dev/input/event6> axes invertion: X is 0, Y is 0
[INFO   ] [MTD         ] </dev/input/event6> rotation set to 0

A seguinte janela mostra!

Alguém sabe o que estou fazendo de errado? Estas são minhas permissões para/dev/input/event6

crwxrwxr-- 1 root input 13, 70 Sep 11 23:47 /dev/input/event6

Muito obrigado!