matplotlib Annotation标注

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.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.scatter(x0, y0, s=50, color='b')
plt.plot([x0, x0], [y0,0], 'k--', lw=2.5)

# 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()