Ubuntu16.04 自带Python2和Python3

$ python --version
Python 2.7.12
$ python3 --version
Python 3.5.2

1. pip环境

1.1. 安装pip

默认pip没有安装，输入pip和pip3，会提示你要安装对应的包

$ pip
The program 'pip' is currently not installed. You can install it by typing:
apt install python-pip
$ pip3
The program 'pip3' is currently not installed. You can install it by typing:
apt install python3-pip

安装pip

1 2	apt-get install python-pip apt-get install python3-pip

检查是否安装成功

$ pip --version
pip 8.1.1 from /usr/lib/python2.7/dist-packages (python 2.7)
$ pip3 --version
pip 8.1.1 from /usr/lib/python3/dist-packages (python 3.5)

1.2. 更新pip

1 2	python -m pip install --upgrade pip python3 -m pip install --upgrade pip

1.2.1. 错误 Traceback (most recent call last): File “/usr/bin/pip”

更新pip之后，可能会出现以下问题，这是pip的一个BUG

$ pip
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
ImportError: cannot import name 'main'
$ pip3
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
ImportError: cannot import name 'main'

编辑 /usr/bin/pip 和 /usr/bin/pip3

# ==============  以下是原本的内容
from pip import main
if __name__ == '__main__':
    sys.exit(main())
# ==============  以下是修改之后的内容
from pip import __main__   # 修改
if __name__ == '__main__':  
    sys.exit(__main__._main())  # 修改

2. 默认Python

Ubuntu下，python命令对应py2，python3命令对应py3

2.1. 利用alternatives机制修改默认python

修改python3为默认，数字大的优先级高

1 2	update-alternatives --install /usr/bin/python python /usr/bin/python2 100 update-alternatives --install /usr/bin/python python /usr/bin/python3 150

设置之后，python和pip都默认对应py3