解决导入matplotlib的RuntimeError: Python is not installed as a framework.

import matplotlib.pyplot as plt
报错：
RuntimeError: Python is not installed as a framework. The Mac OS X backend will not be able to function correctly if Python is not installed as a framework. See the Python documentation for more information on installing Python as a framework on Mac OS X. Please either reinstall Python as a framework, or try one of the other backends.

解决方法：

1. 当pip安装matplotlib后会存在目录： ~/.matplotlib
2. 在上面的目录下新建一个文件并添加内容
   文件：~/.matplotlib/matplotlibrc
   文本内容：backend: TkAgg
3. 保存后重新执行导入即可解决

该问题在stackoverflow的页面：https://stackoverflow.com/questions/21784641/installation-issue-with-matplotlib-python

另一种是这样
import matplotlib
matplotlib.use('TkAgg')
import matplotlib.pyplot as plt