绘制log（）函数图像，并在图上标注选定的两个点
import math
import matplotlib.pyplot as plt
if __name__ == '__main__':
x = [float(i)/200.0 for i in range(1,400)]
y = [math.log(i) for i in x]
plt.plot(x,y,'r-',linewidth=3, label= 'log Curve')
a = [x[30],x[205]]
b = [y[30],y[205]]
plt.plot(a,b,'g-',linewidth=2)
plt.plot(a,b,'b*',markersize=15,alpha=0.75)
plt.legend(loc='upper left')
plt.grid(True)
plt.xlabel('x')
plt.ylabel('log(x)')
plt.show()
运行结果如下所示：
