Python使用matplotlib实现在坐标系中画一个矩形的方法

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()