一. 添加图示图例

1. 代码：

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(-3, 3, 50)
y1 = 2*x + 1
y2 = x**2

plt.figure()
# set x limits
plt.xlim((-1, 2))
plt.ylim((-2, 3))

# set new sticks
new_sticks = np.linspace(-1, 2, 5)
plt.xticks(new_sticks)
# set tick labels
plt.yticks([-2, -1.8, -1, 1.22, 3],
           [r$really bad$, r$bad$, r$normal$, r$good$, r$really good$])

l1, = plt.plot(x, y1, label=linear line)
l2, = plt.plot(x, y2, color=red, linewidth=1.0, linestyle=--, label=square line)

plt.legend(loc=lower right) # 图例显示在右下角
# plt.legend(handles=[l1, l2], labels=[up, down],  loc=best) 这是对于参数的介绍，主要有三个参数，handles是线段，labels是给线取的名字，loc是图例所在位置
# the "," is very important in here l1, = plt... and l2, = plt... for this step
"""legend( handles=(line1, line2, line3),
           labels=(label1, label2, label3),
           upper right)
    The *loc* location codes are::
          best : 0,          (currently not supported for figure legends)
          upper right  : 1,
          upper left   : 2,
          lower left   : 3,
          lower right  : 4,
          right        : 5,
          center left  : 6,
          center right : 7,
          lower center : 8,
          upper center : 9,
          center       : 10,"""

plt.show()

运行结果：

二.  添加标注

1. 代码：

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.plot([x0, x0,], [0, y0,], k--, linewidth=2.5) # [x0,x0],[0,y0]相当于传了两个点的x坐标以及y坐标，k--定义了颜色为black，线条的形式是虚线
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, this is my tag,
         fontdict={size: 16, color: r})

plt.show()

2. 运行结果