python：matplotlib画图入门

 1 import matplotlib.pyplot as plt
 2 import numpy as np
 3 
 4 if __name__ == ‘__main__‘:
 5 x1 = np.linspace(-3, 3, 15)
 6 y1 = [d**2 for d in x1]
 7 # 画图
 8 plt.plot(x1, y1)
 9 x2 = []
10 y2 = []
11 for i, data in enumerate(y1):
12 if data >= 4:
13 x = x1[i]
14 y = data
15 text = "(%d, %d)" % (x, y)
16 # 给图片添加标注，这里的index实际是x坐标，data为y坐标， text为显示的文本内容
17 plt.text(x, y, text, color = ‘green‘)
18 x2.append(x)
19 y2.append(y)
20 plt.plot(x2, y2, ‘o‘, color=‘green‘)
21 plt.show()

 1 import matplotlib.pyplot as plt
 2 import numpy as np
 3 
 4 if __name__ == ‘__main__‘:
 5 x1 = np.linspace(1, 15, 15)
 6 y1 = [(x**2/40 + x*(0.3**x) + x/20) for x in x1]
 7 # 画图
 8 fig, ax = plt.subplots()
 9 ax.plot(x1, y1)
10 x2 = []
11 y2 = []
12 for i, data in enumerate(y1):
13 if i % 3 ==0:
14 x = x1[i]
15 y = data
16 text = "(%d, %f)" % (x, y)
17 # 给图片添加标注，这里的index实际是x坐标，data为y坐标， text为显示的文本内容
18 plt.text(x, y, text, color = ‘green‘)
19 x2.append(x)
20 y2.append(y)
21 plt.plot(x2, y2, ‘o‘, color=‘green‘)
22 
23 # 指定x轴和y轴的的名称
24 plt.xlabel("date")
25 plt.ylabel("value")
26 # xticks指定了在坐标轴上哪些位置显示label
27 xticks = x1[0::3]
28 # xticklabels指定了label的具体内容,在这里就是日期
29 xticklabels = [‘2016-03-0‘+str((n-1)*3+1) for n in range(1,len(xticks)+1)]
30 ax.set_xticks(xticks)
31 ax.set_xticklabels(xticklabels, rotation=15)
32 plt.show()