'Set the draggable state -- if state is
* None : toggle the current state
* True : turn draggable on
* False : turn draggable off
If draggable is on, you can drag the legend on the canvas with
the mouse.  The DraggableLegend helper instance is returned if
draggable is on.
The update parameter control which parameter of the legend changes
when dragged. If update is "loc", the *loc* parameter of the legend
is changed. If "bbox", the *bbox_to_anchor* parameter is changed.'

def draggable(self, state=None, use_blit=False, update=u'loc'):

    is_draggable = (self._draggable is not None)
    if (state is None):
        state = (not is_draggable)
    if state:
        if (self._draggable is None):
            self._draggable = DraggableLegend(self, use_blit, update=update)
    else:
        if (self._draggable is not None):
            self._draggable.disconnect()
        self._draggable = None
    return self._draggable
