Use mouse to draw a shape on canvas，shapecanvas,from Tkinter

Use mouse to draw a shape on canvas，shapecanvas,from Tkinter

from Tkinter import *trace = 0 class CanvasEventsDemo:     def __init__(self, parent=None):        canvas = Canvas(width=300, height=300, bg='beige')         canvas.pack()        canvas.bind('<ButtonPress-1>', self.onStart)           canvas.bind('<B1-Motion>',     self.onGrow)             canvas.bind('<Double-1>',      self.onClear)             canvas.bind('<ButtonPress-3>', self.onMove)             self.canvas = canvas        self.drawn  = None        self.kinds = [canvas.create_oval, canvas.create_rectangle]    def onStart(self, event):        self.shape = self.kinds[0]        self.kinds = self.kinds[1:] + self.kinds[:1]              self.start = event        self.drawn = None    def onGrow(self, event):                                   canvas = event.widget        if self.drawn: canvas.delete(self.drawn)        objectId = self.shape(self.start.x, self.start.y, event.x, event.y)        if trace: print objectId        self.drawn = objectId    def onClear(self, event):        event.widget.delete('all')                         def onMove(self, event):        if self.drawn:                                               if trace: print self.drawn            canvas = event.widget            diffX, diffY = (event.x - self.start.x), (event.y - self.start.y)            canvas.move(self.drawn, diffX, diffY)            self.start = eventif __name__ == '__main__':    CanvasEventsDemo()    mainloop()