import matplotlib.pyplot as plt出错

>>>import matplotlib.pyplot as plt
/usr/lib/python2.7/dist-packages/matplotlib/font_manager.py:273: UserWarning: Matplotlib is building the font cache using fc-list. This may take a moment.
  warnings.warn('Matplotlib is building the font cache using fc-list. This may take a moment.')

在第八讲中,导入这个模块出错
解决:

找到缓存目录
删除~/.cache/matplotlib下面的缓存

 deleted ~/.cache/matplotlib/fontList.cache

但是，当我准备删的时候，再import matplotlib时时没有出错,不知道具体的原因是什么