演示matplotlib中,如何在坐标系中画一个矩形

演示matplotlib中,如何在坐标系中画一个矩形

import matplotlib.pyplot as plt 
from matplotlib.patches import Rectangle  
class Annotate(object):
    def __init__(self):
        self.ax = plt.gca()
        self.rect = Rectangle((0,0), 1, 1)
        self.x0 = None         
        self.y0 = None         
        self.x1 = None         
        self.y1 = None         
        self.ax.add_patch(self.rect)
        self.ax.figure.canvas.mpl_connect('button_press_event', self.on_press)
        self.ax.figure.canvas.mpl_connect('button_release_event', self.on_release)
       
   
    def on_press(self, event):
        print 'press'         
        self.x0 = event.xdata         
        self.y0 = event.ydata      
       
       
    def on_release(self, event):         
        print 'release'         
        self.x1 = event.xdata         
        self.y1 = event.ydata         
        self.rect.set_width(self.x1 - self.x0)
        self.rect.set_height(self.y1 - self.y0)         
        self.rect.set_xy((self.x0, self.y0))         
        self.ax.figure.canvas.draw()  
       
       
a = Annotate() 
plt.show() 

如下图所示