报错提示ImportError: No module named ‘pip._internal’：
nuc@xy:~/Theano$ sudo pip3 install keras
Traceback (most recent call last):
File "/usr/local/bin/pip3", line 7, in <module>
from pip._internal.cli.main import main
ImportError: No module named 'pip._internal'
经过多方查找，终于通过以下方式解决：
wget https://bootstrap.pypa.io/get-pip.py --no-check-certificate
sudo python get-pip.py
之后成功安装keras。