Annotation标注

# View more python tutorials on my Youtube and Youku channel!!!
 
# Youtube video tutorial: https://www.youtube.com/channel/UCdyjiB5H8Pu7aDTNVXTTpcg
# Youku video tutorial: http://i.youku.com/pythontutorial
 
# 8 - annotation
"""
Please note, this script is for python3+.
If you are using python2+, please modify it accordingly.
 
Tutorial reference:
http://www.scipy-lectures.org/intro/matplotlib/matplotlib.html
 
Mathematical expressions:
http://matplotlib.org/users/mathtext.html#mathtext-tutorial
"""
 
import matplotlib.pyplot as plt
import numpy as np
 
x = np.linspace(-3, 3, 50)
y = 2*x + 1
 
plt.figure(num=1, figsize=(8, 5),)
plt.plot(x, y,)
 
ax = plt.gca()
ax.spines['right'].set_color('none')
ax.spines['top'].set_color('none')
ax.spines['top'].set_color('none')
ax.xaxis.set_ticks_position('bottom')
ax.spines['bottom'].set_position(('data', 0))
ax.yaxis.set_ticks_position('left')
ax.spines['left'].set_position(('data', 0))
 
x0 = 1
y0 = 2*x0 + 1
plt.plot([x0, x0,], [0, y0,], 'k--', linewidth=2.5)
plt.scatter([x0, ], [y0, ], s=50, color='b')
 
# method 1:
#####################
plt.annotate(r'$2x+1=%s$' % y0, xy=(x0, y0), xycoords='data', xytext=(+30, -30),
             textcoords='offset points', fontsize=16,
             arrowprops=dict(arrowstyle='->', connectionstyle="arc3,rad=.2"))
 
# method 2:
########################
plt.text(-3.7, 3, r'$This\ is\ the\ some\ text. \mu\ \sigma_i\ \alpha_t$',
         fontdict={'size': 16, 'color': 'r'})
 
plt.show()