virtualenv 创建“独立”的Python运行环境的原理
把原始 Python 环境复制一份到 virtualenv 的环境，用命令 source venv/bin/activate 进入一个 virtualenv 环境时，virtualenv 会修改相关环境变量，让命令 python 和 pip 均指向当前的 virtualenv 环境。
VirtaulenvWrapper 是 virtualenv 的扩展包，用于更方便管理虚拟环境：
- 将所有虚拟环境整合在一个目录下
- 管理（新增，删除，复制）虚拟环境
- 方便切换虚拟环境
- 安装 virtualenv
pip3 install virtualenv
- 安装 virtualenvwrapper
pip3 install virtualenvwrapper
- 配置 virtualenvwrapper 环境变量（基于用户环境变量
~/.bashrc文件）
# Python VirtualEnv Environment
export VIRTUALENVWRAPPER_PYTHON=$PYTHON_HOME/bin/python3
export WORKON_HOME=/home/codedancing/ProEnv/PythonEnvs/
source /home/codedancing/ProEnv/Python/python3.7.6/bin/virtualenvwrapper.sh
编辑完成之后刷新环境变量：
source ~/.bashrc
出现下面的输出，则配置完成：
[codedancing@centos PythonEnvs]$ source ~/.bashrc
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/premkproject
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/postmkproject
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/initialize
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/premkvirtualenv
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/postmkvirtualenv
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/prermvirtualenv
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/postrmvirtualenv
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/predeactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/postdeactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/preactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/postactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/get_env_details
WORKON_HOME : 指定虚拟环境存储目录
VIRTUALENVWRAPPER_PYTHON：指定 virtualenvwrapper 的 Python 解释器，不配置可能会导致 virtualenvwrapper 环境配置出现问题：
/usr/bin/python: No module named virtualenvwrapper
virtualenvwrapper.sh: There was a problem running the initialization hooks.
If Python could not import the module virtualenvwrapper.hook_loader,
check that virtualenvwrapper has been installed for
VIRTUALENVWRAPPER_PYTHON=/usr/bin/python and that PATH is
- 创建 Python 虚拟环境
指定虚拟环境名为 python3.7，执行 mkvirtualenv python3.7
[codedancing@centos PythonEnvs]$ mkvirtualenv python3.7
Using base prefix '/home/jialei/ProEnv/Python/python3.7.6'
New python executable in /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/python3.7
Also creating executable in /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/python
Installing setuptools, pip, wheel...
done.
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/predeactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/postdeactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/preactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/postactivate
virtualenvwrapper.user_scripts creating /home/codedancing/ProEnv/PythonEnvs/python3.7/bin/get_env_details
并自动切换到虚拟环境，查看虚拟环境列表：
(python3.7) [codedancing@centos PythonEnvs]$ lsvirtualenv
python3.7
=========
查看pip3：
(python3.7) [codedancing@centos PythonEnvs]$ pip3 -V
pip 19.3.1 from /home/codedancing/ProEnv/PythonEnvs/python3.7/lib/python3.7/site-packages/pip (python 3.7)
退出虚拟环境，查看 pip3：
(python3.7) [codedancing@centos PythonEnvs]$ deactivate
[codedancing@centos PythonEnvs]$ pip3 -V
pip 19.2.3 from /home/codedancing/ProEnv/Python/python3.7.6/lib/python3.7/site-packages/pip (python 3.7)
- 常用命令
所有的命令可使用：virtualenvwrapper --help 进行查看
创建基本环境：mkvirtualenv [环境名]
删除环境：rmvirtualenv [环境名]
激活环境：workon [环境名]
退出环境：deactivate
列出所有环境：lsvirtualenv -b
