widgets for row-/colspan grid layout

from kivy.uix.widget import Widget
from kivy.properties import BoundedNumericProperty, ListProperty

class SpannableWidget(Widget):
    """Widget with rowspan/colspan attributes able to span across rows/cols"""

    rowspan = BoundedNumericProperty(1, min=1)
    colspan = BoundedNumericProperty(1, min=1)

    # list of widgets, representing extention by y-axis
    _rowspan = ListProperty([])
    # list of widgets, representing extention by x-axis
    _colspan = ListProperty([])

    def on_parent(self, instance, parent):
        """Clear extention widget lists when widget is inserted/removed

        @param instance: instance, that fired the event
        @param parent: new C{self.parent} value

        """
        for _widget in self._rowspan:
            _widget.unbind(height=self.update, y=self.update)
        self._rowspan = []

        for _widget in self._colspan:
            _widget.unbind(width=self.update, x=self.update)
        self._colspan = []

    def update(self, *largs):
        """Update widget size and position

        @param largs: arguments of the property change event (not used)

        """
        _widget = None
        _height = self.parent.height
        for _widget in self._rowspan:
            _height += _widget.height
        self.height = _height
        if _widget:
            # Stretch widget vertically specifying its y (lower) bound
            self.y = _widget.y
            pass
        self.width = self.parent.width
        for _widget in self._colspan:
            # Stretch widget horizontally increasing its width
            self.width += _widget.width
        # Align widget with parent (C{Placeholder}) by x axis
        self.x = self.parent.x


class Span(Widget):
    """Widget taking place for rowspan/colspan of other widgets"""

    pass


class Placeholder(Widget):
    """Widget holding single child

    Represents an empty matrix cell.

    Used to fill C{terminal.layout.Grid.children} list with empty spaces,
    widgets can be inserted into those later.

    """
    def add_widget(self, widget):
        """Insert one child and stub this method"""
        if self.children:
            return
        super(Placeholder, self).add_widget(widget)
        self.bind(
            size=widget.setter("size"),
            pos=widget.setter("pos"))