gistfile1.py

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

Builder.load_string("""
<TestWidget>
    Label:
        id: my_label
        text: "WASSUP"
        font_size: 20
        font_name: "tower_print.otf"
""")

class TestWidget(Widget):
    pass

class TestApp(App):

    def build(self):
        widget = TestWidget()
        return widget

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