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2011-01-20 10:49

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virtualenv 的作用相当于 Sandbox，它通过隔离包目录和系统环境参数来实现多个相对独立的虚拟环境。如此可避免过多的第三方库因版本依赖造成问题。同时每个独立的虚拟环境只需通过打包即可分发，也大大方便了系统部署。

$ sudo easy_install virtualenv

现在我们可以创建虚拟环境了。

$ virtualenv test1New python executable in test1/bin/pythonInstalling setuptools............done.

我们可以看到虚拟目录下已经被安装了基本所需的运行环境。

$ ls test1/binactivate  activate_this.py  easy_install  easy_install-2.6  pip  python$ ls test1/include/python2.6$ ls test1/libpython2.6$ 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.pycabc.py       encodings        locale.py        posixpath.pyc  sre_constants.py   types.pyabc.pyc      fnmatch.py       locale.pyc       re.py          sre_constants.pyc  types.pyccodecs.py    fnmatch.pyc      ntpath.py        re.pyc         sre_parse.py       UserDict.pycodecs.pyc   genericpath.py   ntpath.pyc       site-packages  sre_parse.pyc      UserDict.pycconfig       genericpath.pyc  orig-prefix.txt  site.py        sre.py             warnings.pycopy_reg.py  lib-dynload      os.py            site.pyc       sre.pyc            warnings.pyc

进入 test1 目录，激活虚拟环境。

$ cd test1test1$ 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$ pythonPython 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)[GCC 4.4.3] on linux2Type "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" 激活以后，命令提示行多了一个 "(test1)" 前缀，同时 python 和 easy_install 默认会使用虚拟环境 bin 目录下的程序。sys.path 显示当前虚拟环境的库目录被添加到搜索路径列表中。

(test1)$ easy_install MySQL-pythonSearching for MySQL-pythonReading Reading Best match: MySQL-python 1.2.3c1Downloading Processing downloadRunning MySQL-python-1.2.3c1/setup.py -q bdist_egg --dist-dir /tmp/easy_install-Em0wfb/MySQL-python-1.2.3c1/egg-dist-tmp-vzoJ2tIn file included from _mysql.c:36:/usr/include/mysql/my_config.h:1050:1: warning: "HAVE_WCSCOLL" redefinedIn 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 definitionzip_safe flag not set; analyzing archive contents...Adding MySQL-python 1.2.3c1 to easy-install.pth fileInstalled /home/yuhen/projects/python/test1/lib/python2.6/site-packages/MySQL_python-1.2.3c1-py2.6-linux-x86_64.eggProcessing dependencies for MySQL-pythonFinished 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.eggdrwxr-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 被安装到了虚拟环境中，且 easy-install.pth 中正确添加了 egg 搜索路径。

最后我们可以用 "deactivate" 命令退出虚拟环境。

(test1)test1$ deactivate

在创建虚拟环境时，我们可以添加 "--no-site-packages" 参数指示虚拟环境不要访问 global site-packages。

$ virtualenv --no-site-packages test2New python executable in test2/bin/pythonInstalling setuptools............done.$ cd test2test2$ 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']>>>

搜索路径中除了 Python 基本库路径外，已经没有了 global site-packages。这样即便我们在安装了大量开发包的的系统里，也可以隔离出一个干净的测试环境。

要判断一个虚拟环境是否 --no-site-packages，除了检查 sys.path 外，还可以通过 "lib/python2.6/no-global-site-packages.txt" 文件来判断。