Backend TkAgg is interactive backend. Turning interactive mode on.

matplotlib的默认backend是TkAgg，而FltkAgg, GTK, GTKAgg, GTKCairo, TkAgg , Wx or WxAgg这几个backend都要求有GUI图形界面的。

import matplotlib.pyplot as plt
Backend TkAgg is interactive backend. Turning interactive mode on.

plt.get_backend()
Out[3]: u'TkAgg'

解决方法：指定不需要GUI的backend（Agg, Cairo, PS, PDF or SVG）

import matplotlib.pyplot as plt
plt.switch_backend('agg')

 

From： RuntimeError: Invalid DISPLAY variable