Python virtualenv - 青面獠牙的城堡 - 博客频道 - CSDN.NET
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 test1 New python executable in test1/bin/python Installing 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/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
进入 test1 目录，激活虚拟环境。$ 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" 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-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 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。