ubuntu18.04自带python3，但是没有python2，pip2，pip3。
sudo apt install python2.7 #安装python2.7
sudo apt install python-minimal
sudo apt install curl
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
sudo python3 get-pip.py #安装pip3
sudo python2 get-pip.py #安装pip3
sudo apt install python-testresources #防止pip2出错
sudo apt install python3-testresources #防止pip3出错
sudo pip3 install --upgrade pip #升级pip3
sudo pip2 install --upgrade pip #升级pip2
此时pip和python并不知道指向2还是3，需要自己修改。我们使用alias来设置别名。我要让pip和python都指向3
whereis pip
pip: /usr/local/bin/pip /usr/local/bin/pip3.6 /usr/local/bin/pip2.7
whereis python
python: /usr/bin/python2.7 /usr/bin/python2.7-config /usr/bin/python3.6m /usr/bin/python3.6 /usr/bin/python3.6m-config /usr/bin/python3.6-config /usr/bin/python /usr/lib/python2.7 /usr/lib/python3.7 /usr/lib/python3.6 /etc/python2.7 /etc/python3.6 /etc/python /usr/local/lib/python2.7 /usr/local/lib/python3.6 /usr/include/python2.7 /usr/include/python3.6m /usr/include/python3.6 /usr/share/python /usr/share/man/man1/python.1.gz
可见pip3在：
/usr/local/bin/pip3.6
python在：
/usr/bin/python3.6
自定义alias别名：
gedit ~/.bashrc
打开文件后，在最后一行加：
alias pip=/usr/local/bin/pip3.6
alias python=/usr/bin/python3.6
然后更新环境：
source ~/.bashrc
