Just an example of some kv used in practice

gistfile1.txt

                # meanwhile in some widget tree I create an instance and
                # set the property in that specific tree for the specific ColorSel instance
                ColorSel:
                    title: 'high color'
                    # passing in the attribute that will be bound inside kv
                    bind_color: 'ebbh'



<ColorSel@RelativeLayout>:
    swatch: swatch
    hue_slider: hue_slider
    val_slider: val_slider
    Label:
        halign: 'left'
        valign: 'middle'
        text_size: self.size
        font_size: self.height * 0.7
        size_hint: d_ctl.l1_sh
        pos_hint: d_ctl.l1_ph
        text: 'color'
    Slider:
        id: hue_slider
        range: (0., 1.)
        size_hint: d_ctl.cs1_sh
        pos_hint: d_ctl.cs1_ph
        on_value: root.hue = self.value
    Label:
        halign: 'left'
        valign: 'middle'
        size_hint: d_ctl.l2_sh
        pos_hint: d_ctl.l2_ph
        text: 'light'
        text_size: self.size
        font_size: self.height * 0.7
    Slider:
        id: val_slider
        range: (0., 1.)
        size_hint: d_ctl.cs2_sh
        pos_hint: d_ctl.cs2_ph
        on_value: root.val = self.value
    RelativeLayout:
        size_hint: d_ctl.swatch_sh 
        pos_hint: d_ctl.swatch_ph
        Swatch:
            id: swatch
        Label:
            halign: 'center'
            valign: 'middle'
            size_hint: (0.9, 0.9)
            pos_hint: {'x' : 0.05, 'y' : 0.05}
            text: root.title
            text_size: self.size
            font_size: self.height * 0.5


class ColorSel(RelativeLayout):
    hue = NumericProperty()
    val = NumericProperty()
    title = StringProperty()
    bind_color = StringProperty()

    def on_hue(self, i, hue):
        # here's where I'm using the value set in the kv file
        getattr(c_ctl, self.bind_color)[0] = hue

    def on_val(self, i, val):
        # here's where I'm using the value set in the kv file
        getattr(c_ctl, self.bind_color)[2] = val

    def on_bind_color(self, i, color):
        # here's where I'm using the value set in the kv file
        self.hue = getattr(c_ctl, color)[0]
        self.val = getattr(c_ctl, color)[2]
        self.hue_slider.value = self.hue
        self.val_slider.value = self.val
        self.swatch.color = getattr(c_ctl, color)
        # this use of kwargs unpacking is pretty damned slick
        # if I must say so.  color is a string, but I need
        # the equivalent of passing in a named argument...so a dictionary, unpacked
        c_ctl.bind(**{color : self.swatch.setter('color')})