'Resize the canvas the turtles are drawing on. Does
not alter the drawing window.'

def _resize(self, canvwidth=None, canvheight=None, bg=None):

    if (not isinstance(self.cv, ScrolledCanvas)):
        return (self.canvwidth, self.canvheight)
    if (canvwidth is canvheight is bg is None):
        return (self.cv.canvwidth, self.cv.canvheight)
    if (canvwidth is not None):
        self.canvwidth = canvwidth
    if (canvheight is not None):
        self.canvheight = canvheight
    self.cv.reset(canvwidth, canvheight, bg)
