python中類似RVM的virtualenv

virtualenv 的作用相當於 Sandbox，它通過隔離包目錄和系統內容參數來實現多個相對獨立的虛擬環境。如此可避免過多的第三方庫因版本依賴造成問題。同時每個獨立的虛擬環境只需通過打包即可分發，也大大方便了系統部署。

$ sudo easy_install virtualenv

現在我們可以建立虛擬環境了。

$ virtualenv test1

New python executable in test1/bin/python
Installing setuptools............done.

我們可以看到虛擬目錄下已經被安裝了基本所需的運行環境。

$ ls test1/bin
activate  activate_this.py  easy_install  easy_install-2.6  pip  python

$ ls test1/include/
python2.6

$ ls test1/lib
python2.6

$ ls test1/lib/python2.6/
_abcoll.py   copy_reg.pyc     linecache.py     os.pyc         sre_compile.py     stat.py
_abcoll.pyc  distutils        linecache.pyc    posixpath.py   sre_compile.pyc    stat.pyc
abc.py       encodings        locale.py        posixpath.pyc  sre_constants.py   types.py
abc.pyc      fnmatch.py       locale.pyc       re.py          sre_constants.pyc  types.pyc
codecs.py    fnmatch.pyc      ntpath.py        re.pyc         sre_parse.py       UserDict.py
codecs.pyc   genericpath.py   ntpath.pyc       site-packages  sre_parse.pyc      UserDict.pyc
config       genericpath.pyc  orig-prefix.txt  site.py        sre.py             warnings.py
copy_reg.py  lib-dynload      os.py            site.pyc       sre.pyc            warnings.pyc

進入 test1 目錄，啟用虛擬環境。

$ cd test1

test1$ source bin/activate

(test)test1$ which python
/home/yuhen/projects/test1/bin/python

(test)test1$ which easy_install
/home/yuhen/projects/test1/bin/easy_install

(test1)test1$ python

Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.

>>> import sys
>>> sys.path
['', 
'/home/yuhen/projects/test1/lib/python2.6/site-packages/setuptools-0.6c11-py2.6.egg', 
'/home/yuhen/projects/test1/lib/python2.6/site-packages/pip-0.7.2-py2.6.egg', 
'/home/yuhen/projects/test1/lib/python2.6', 
'/home/yuhen/projects/test1/lib/python2.6/plat-linux2', 
'/home/yuhen/projects/test1/lib/python2.6/lib-tk', 
'/home/yuhen/projects/test1/lib/python2.6/lib-old', 
'/home/yuhen/projects/test1/lib/python2.6/lib-dynload', 
'/usr/lib/python2.6', 
'/usr/lib64/python2.6', 
'/usr/lib/python2.6/plat-linux2', 
'/usr/lib/python2.6/lib-tk', 
'/usr/lib64/python2.6/lib-tk', 
'/home/yuhen/projects/test1/lib/python2.6/site-packages', 
'/usr/local/lib/python2.6/dist-packages/virtualenv-1.4.9-py2.6.egg', 
'/usr/local/lib/python2.6/dist-packages/simplejson-2.1.1-py2.6-linux-x86_64.egg', 
'/usr/local/lib/python2.6/site-packages', 
'/usr/local/lib/python2.6/dist-packages', 
'/usr/lib/python2.6/dist-packages', 
'/usr/lib/pymodules/python2.6', 
'/usr/lib/pymodules/python2.6/gtk-2.0', 
'/usr/lib/python2.6/dist-packages/wx-2.8-gtk2-unicode']
>>>

可以看到使用 "souce bin/active" 啟用以後，命令提示行多了一個 "(test1)" 首碼，同時 python 和 easy_install 預設會使用虛擬環境 bin 目錄下的程式。sys.path 顯示當前虛擬環境的庫目錄被添加到搜尋路徑列表中。

(test1)$ easy_install MySQL-python
Searching for MySQL-python
Reading http://pypi.python.org/simple/MySQL-python/
Reading http://sourceforge.net/projects/mysql-python
Best match: MySQL-python 1.2.3c1
Downloading http://sourceforge.net/.../1.2.3c1/MySQL-python-1.2.3c1.tar.gz/download
Processing download
Running MySQL-python-1.2.3c1/setup.py -q bdist_egg --dist-dir /tmp/easy_install-Em0wfb/MySQL-python-1.2.3c1/egg-dist-tmp-vzoJ2t
In file included from _mysql.c:36:
/usr/include/mysql/my_config.h:1050:1: warning: "HAVE_WCSCOLL" redefined
In file included from /usr/include/python2.6/Python.h:8,
from pymemcompat.h:10,
from _mysql.c:29:
/usr/include/python2.6/pyconfig.h:808:1: warning: this is the location of the previous definition
zip_safe flag not set; analyzing archive contents...
Adding MySQL-python 1.2.3c1 to easy-install.pth file

Installed /home/yuhen/projects/python/test1/lib/python2.6/site-packages/MySQL_python-1.2.3c1-py2.6-linux-x86_64.egg
Processing dependencies for MySQL-python
Finished processing dependencies for MySQL-python

(test1)$ ls -l lib/python2.6/site-packages/
total 444
-rw-r--r-- 1 yuhen yuhen    283 2010-06-02 09:46 easy-install.pth
-rw-r--r-- 1 yuhen yuhen 106325 2010-06-02 09:46 MySQL_python-1.2.3c1-py2.6-linux-x86_64.egg
drwxr-xr-x 4 yuhen yuhen   4096 2010-06-02 09:45 pip-0.7.2-py2.6.egg
-rw-r--r-- 1 yuhen yuhen 333447 2010-06-01 23:58 setuptools-0.6c11-py2.6.egg
-rw-r--r-- 1 yuhen yuhen     30 2010-06-02 09:45 setuptools.pth

(test1)$ cat lib/python2.6/site-packages/setuptools.pth
./setuptools-0.6c11-py2.6.egg

(test1)$ python
>>> import MySQLdb
>>> MySQLdb.version_info
(1, 2, 3, 'gamma', 1)
>>>

MySQL-python 被安裝到了虛擬環境中，且 easy-install.pth 中正確添加了 egg 搜尋路徑。

最後我們可以用 "deactivate" 命令退出虛擬環境。

(test1)test1$ deactivate

在建立虛擬環境時，我們可以添加 "--no-site-packages" 參數指示虛擬環境不要訪問 global site-packages。

$ virtualenv --no-site-packages test2
New python executable in test2/bin/python
Installing setuptools............done.

$ cd test2

test2$ source bin/activate

(test2)test2$ python
>>> import sys
>>> sys.path
['', 
'/home/yuhen/projects/python/test2/lib/python2.6/site-packages/setuptools-0.6c11-py2.6.egg',
'/home/yuhen/projects/python/test2/lib/python2.6/site-packages/pip-0.7.2-py2.6.egg', 
'/home/yuhen/projects/python/test2/lib/python2.6', 
'/home/yuhen/projects/python/test2/lib/python2.6/plat-linux2', 
'/home/yuhen/projects/python/test2/lib/python2.6/lib-tk', 
'/home/yuhen/projects/python/test2/lib/python2.6/lib-old', 
'/home/yuhen/projects/python/test2/lib/python2.6/lib-dynload', 
'/usr/lib/python2.6', 
'/usr/lib64/python2.6', 
'/usr/lib/python2.6/plat-linux2', 
'/usr/lib/python2.6/lib-tk', 
'/usr/lib64/python2.6/lib-tk', 
'/home/yuhen/projects/python/test2/lib/python2.6/site-packages']
>>>

搜尋路徑中除了 Python 基本庫路徑外，已經沒有了 global site-packages。這樣即便我們在安裝了大量開發包的的系統裡，也可以隔離出一個乾淨的測試環境。

要判斷一個虛擬環境是否 --no-site-packages，除了檢查 sys.path 外，還可以通過 "lib/python2.6/no-global-site-packages.txt" 檔案來判斷。