Python VIRTUAL ENV

Python virtual enviroment 提供一个独立的 python 运行环境，用来解决类似 Windows 上的 DLL HELL 问题。将应用的依赖和版本等隔离开来。每个应用有自己的隔离环境。

Python 在用的版本有很多， 2.6， 2.7， 3.5， 3.6 等等。每一个依赖也可能很多版本，中间很多兼容性问题。如果将他们全都放到一起，就会产生 DLL HELL 的问题。

➜  module2 l /usr/local/lib/python2.7/site-packages
total 4392
drwxr-xr-x  95 lucas  admin   3.0K Nov 24 18:00 .
drwxr-xr-x   4 lucas  admin   128B Nov  1 20:26 ..
drwxr-xr-x   9 lucas  admin   288B Nov  3 23:25 astroid-1.5.3.dist-info
drwxr-xr-x   7 lucas  admin   224B Nov  3 23:25 backports
drwxr-xr-x   9 lucas  admin   288B Nov  3 23:25 backports.functools_lru_cache-1.4.dist-info

Install

$ [sudo] pip install virtualenv

也可以安装源代码到本地，这样不需要 sudo 权限

$ python virtualenv.py myVE
$ ls -lah
total 256K
drwxr-xr-x 10 lucas lucas 4.0K 2017-11-27 16:01 .
drwxr-xr-x  7 lucas lucas 4.0K 2017-11-27 16:01 ..
-rw-r--r--  1 lucas lucas 1.2K 2016-11-16 11:39 AUTHORS.txt
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 bin
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 docs
-rw-r--r--  1 lucas lucas 1.2K 2016-11-16 11:39 LICENSE.txt
-rw-r--r--  1 lucas lucas  345 2016-11-16 11:39 MANIFEST.in
drwxr-xr-x  5 lucas lucas 4.0K 2017-11-27 16:01 myVE
-rw-r--r--  1 lucas lucas 3.4K 2016-11-16 11:39 PKG-INFO
-rw-r--r--  1 lucas lucas 1.2K 2016-11-16 11:39 README.rst
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 scripts
-rw-r--r--  1 lucas lucas   88 2016-11-16 11:39 setup.cfg
-rw-r--r--  1 lucas lucas 4.0K 2016-11-16 11:39 setup.py
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 tests
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 virtualenv.egg-info
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 virtualenv_embedded
-rwxr-xr-x  1 lucas lucas  97K 2016-11-16 11:39 virtualenv.py
-rw-r--r--  1 lucas lucas  86K 2017-11-27 16:01 virtualenv.pyc
drwxr-xr-x  2 lucas lucas 4.0K 2016-11-16 11:39 virtualenv_support

核心文件是 virtualenv.py 当然要求相关的类库存在。

使用

➜  /tmp virtualenv ENV
New python executable in /private/tmp/ENV/bin/python2.7
Also creating executable in /private/tmp/ENV/bin/python
Installing setuptools, pip, wheel...done.

➜  /tmp tree -L 2 ENV
ENV
├── bin
│   ├── activate
│   ├── activate.csh
│   ├── activate.fish
│   ├── activate_this.py
│   ├── easy_install
│   ├── easy_install-2.7
│   ├── pip
│   ├── pip2
│   ├── pip2.7
│   ├── python -> python2.7
│   ├── python-config
│   ├── python2 -> python2.7
│   ├── python2.7
│   └── wheel
├── include
│   └── python2.7 -> /usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/include/python2.7
├── lib
│   └── python2.7
└── pip-selfcheck.json

5 directories, 15 files

ENV/lib/ and ENV/include/ are created, containing supporting library files for a new virtualenv python. Packages installed in this environment will live under ENV/lib/pythonX.X/site-packages/.
ENV/bin is created, where executables live - noticeably a new python. Thus running a script with #! /path/to/ENV/bin/python would run that script under this virtualenv’s python.
The crucial packages pip and setuptools are installed, which allow other packages to be easily installed to the environment. This associated pip can be run from ENV/bin/pip.

激活

$ source bin/activate

$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

$ source bin/activate

$ echo $PATH
/home/xx/virtualenv-15.1.0/myVE/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games