我在 Ubuntu 16.04 上使用 python2.7 和 python3.5。将 pip 升级到 v10 后，我无法再使用 pip 安装 python2.7 的软件包。
如何更改 pip 以指向 python2.7？
$ pip -V
pip 10.0.0 from /home/username/.local/lib/python3.5/site-packages/pip (python 3.5)
$ pip3 -V
pip 10.0.0 from /home/username/.local/lib/python3.5/site-packages/pip (python 3.5)
$ which python
/usr/bin/python
$ which python3
/usr/bin/python3
$ python -V
Python 2.7.12
$ python3 -V
Python 3.5.2
$ which pip
/usr/local/bin/pip
$ which pip3
/usr/local/bin/pip3
$ python3 -m pip install some_module
$ python -m pip install some_module
python/python3 -m pip install some_module …