gistfile1.py

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout

Builder.load_string("""
<TestWidget>
    label: label

    Label:
        id: label
        size_hint: .1, .1
        pos_hint: {"x": .5, "y": .5}

        canvas.before:
            Color:
                rgb: .4, .1, .5
            Rectangle:
                size: self.size
                pos: self.pos

            Color:
                rgb: .1, .8, .4
            Line:
                circle: (self.center_x, self.center_y, min(self.width, self.height) / 2)

""")


class TestWidget(FloatLayout):

    def __init__(self):
        FloatLayout.__init__(self)

        self.label.bind(on_touch_down=self.label_down)

    def label_down(self, btn, event):
        print "Label down !"


class TestApp(App):

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

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