import numpy as np
import pandas as pd
import matplotlib.pyplot as plt


df_data = pd.DataFrame(np.random.rand(20, 1), columns=['a'])

fig, axes = plt.subplots()

axes.errorbar(
    df_data.index,
    df_data['a'],
    color='CadetBlue', marker='d')

# Hangs
# axes.vlines(8.5, 0, 1e6, colors='Silver', linestyles='dashed')
# axes.set_ylim((0, 1))

# Works
# axes.vlines(8.5, 0, 1e3, colors='Silver', linestyles='dashed')
# axes.set_ylim((0, 1))

# Works
# axes.vlines(8.5, 0, 1e6, colors='Silver', linestyles='dashed')
# axes.set_ylim((0, 1e1))

print('check A')
plt.savefig('test_image')
print('check B')
plt.close()