Python Virtual Environments

Python虚拟环境可以在独立的地方保持针对不同的工程的依赖需求,通过为它们创建虚拟Python环境.它解决这样的困境,"工程X以来版本1.x,但是工程Y需要4.x".并且你的全局site-packages整洁可控.

virtualenv

virtualenv is a tool to create isolated Python environments.

$ sudo pip install virtualenv

Create a virtual environment for a project
Creates a copy of Python in whichever directory you ran the command in, placing it in a folder named venv.
```
$ cd my_project_folder
$ virtualenv venv
```
use a Python interpreter
use the Python interpreter in /usr/bin/python2.7
```
$ virtualenv -p /usr/bin/python2.7 venv
```
activate the virtual environment
```
$ source venv/bin/activate
```
The name of the current virtual environment will now appear on the left of the prompt (e.g. (venv)Your-Computer:your_project UserName$) to let you know that it’s active.
deactivate
```
$ deactivate
```
delete a virtual environment
delete its folder
```
rm -rf venv
```

“freeze” the current state of the environment packages
```
$ pip freeze > requirements.txt
```
re-create the environment
```
$ pip install -r requirements.txt
```

virtualenvwrapper provides a set of commands which makes working with virtual environments much more pleasant.

$ sudo pip install virtualenvwrapper
$ export WORKON_HOME=~/Envs
$ mkdir -p $WORKON_HOME
$ source /usr/local/bin/virtualenvwrapper.sh

export WORKON_HOME=~/Envs
source /usr/local/bin/virtualenvwrapper.sh

Create a virtual environment
This creates the venv folder inside ~/Envs.
```
$ mkvirtualenv env1
```
Work on a virtual environment
```
workon venv
```
Deactivating
```
$ deactivate
```
Delete
```
$ rmvirtualenv venv
```

lsvirtualenv List all of the environments.
cdvirtualenv Navigate into the directory of the currently activated virtual environment.
cdsitepackages Navigate into currently activated site-packages directory.
lssitepackages Shows contents of site-packages directory.

When you cd into a directory containing a .env, autoenv automagically activates the environment.

$ git clone git://github.com/kennethreitz/autoenv.git ~/.autoenv
$ echo 'source ~/.autoenv/activate.sh' >> ~/.bashrc