gistfile1.txt

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

Builder.load_string("""
<RotatingWidget>:
    on_size: self.reset_child()
    on_pos: self.reset_child()
    canvas.before:
        PushMatrix:
        Rotate:
            angle: 90
            origin: (self.right, self.y)
            axis: 0, 0, 1
    canvas.after:
        PopMatrix:
""")

class RotatingWidget(Widget):

    def reset_child(self):
        """Reposition our child so that it displays correctly."""

        if not self.children:
            print('No children to reset')
            return

        child = self.children[0]

        child.width = self.height
        child.height = self.width
        child.pos = (self.right, self.y)


if __name__ == "__main__":
    from kivy.base import runTouchApp
    from kivy.uix.button import Button

    rw = RotatingWidget()
    rw.add_widget(Button(text='hello world'))

    runTouchApp(rw)