'Start a new link.'

def startLink(self, event):

    if (event.widget not in self.widgetToItem):
        return
    w = event.widget
    item = self.widgetToItem[w]
    (x, y) = self.canvas.coords(item)
    self.link = self.canvas.create_line(x, y, x, y, width=4, fill='blue', tag='link')
    (self.linkx, self.linky) = (x, y)
    self.linkWidget = w
    self.linkItem = item
