Matplotlib：错误栏缺少行

Question

我想绘制一些东西，但输出不是我想要的。我希望我的照片上有红线，但我没有在文档中找到参数。

import matplotlib.pyplot as plt
import math
import numpy as np

fig, ax = plt.subplots()
files = ['N30.dat', 'N40.dat', 'N50.dat', 'N60.dat', 'N70.dat', 'N80.dat']
N = 30

plot_list_x = []
plot_list_y = []

for fname in files:
    data = np.loadtxt(fname)
    x = [1 for _ in range(10)]
    N += 10

    # mean
    mean = data.mean()
    plt.plot(N, mean, '.')

    plot_list_x.append(N)
    plot_list_y.append(mean)

    # standard derivation
    sd = 0
    for i in data:
        sd += math.pow(i - mean, 2)
    sd = math.sqrt(sd/(N-1))

    # standard error
    se = sd/math.sqrt(N)

    plt.errorbar(N, mean, yerr=sd, fmt='_', ecolor='g', capthick=2)

plt.plot(plot_list_x, plot_list_y, 'g-')

plt.xticks([20, 30, 40, 50, 60, 70, 80, 90, 100])
plt.yticks([0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9])

ax.set_title('Airline Streaming')
ax.set_xlabel('count of clients')
ax.set_ylabel('packet loss')
plt.show()

我想要这个，但是我没有红线就得到了照片。