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" This module is automatically imported during initialization. The automatic import
can be suppressed using the interpreter’s -S option.
Importing this module will append site-specific paths to the module search path and add a few builtins. " Ref[1]
在解释器(interpreter)启动时，site会被自动的导入(imported)。在导入时，site扩展sys.path。
扩展的方式是使用sys.prefix 和 sys.exec_prefix。site.py中PREFIXES的定义如下，Ref[3]:
1 # Prefixes for site-packages; add additional prefixes like /usr/local here 2 PREFIXES = [sys.prefix, sys.exec_prefix]
Q: 那么sys.prefix sys.exec_prefix 和 sys.path 的含义分别是什么呢?
Ref[4]
Demo-1: 查看site.PREFIXES
1 import sys 2 import os 3 import platform 4 import site 5 6 if ‘Windows‘ in platform.platform(): 7 SUFFIXES = [ 8 ‘‘, 9 ‘lib/site-packages‘, 10 ] 11 else: 12 SUFFIXES = [ 13 ‘lib/python%s/site-packages‘ % sys.version[:3], 14 ‘lib/site-python‘, 15 ] 16 17 print ‘Path prefixes:‘ 18 for p in site.PREFIXES: 19 print ‘ ‘, p 20 21 for prefix in sorted(set(site.PREFIXES)): 22 print 23 for suffix in SUFFIXES: 24 path = os.path.join(prefix, suffix).rstrip(os.sep) 25 print path 26 print ‘ exists:‘, os.path.exists(path) 27 print ‘ in path:‘, path in sys.path
http://pymotw.com/2/site/
"In addition to the global site-packages paths, site is responsible for adding the
user-specific locations to the import path." Ref[2]
Q: globale site-package 和 import path分别是什么?
user-specific path是基于USER_BASE的。在USER_BASE中的是site-packages directory，该directory的路径是
USER_SITE。
"The user-specific paths are all based on the USER_BASE directory, which usually
located in a part of the filesystem owned (and writable) by the current user."
A):
Demo-2: 查看 USER_BASE USER_SITE
1 import site 2 3 print ‘Base:‘, site.USER_BASE 4 print ‘Site:‘, site.USER_SITE
输出是：
"
Base: /Users/XiaoKL/Library/Python/2.7
Site: /Users/XiaoKL/Library/Python/2.7/lib/python/site-packages
"
USER_BASE可以由环境变量PYTHONUSERBASE来设置。
B): 命令查看USER_BASE USER_SITE：
$ python -m site --user-base
$ python -m site --user-site
$ PYTHONUSERBASE=/tmp/$USER python -m site --user-base
$ PYTHONUSERBASE=/tmp/$USER python -m site --user-site
python的-m module-name:
"-m module-name
Searches sys.path for the named module and runs the correspond-
ing .py file as a script. " Ref[man python2.7]
The user directory can also be explicitly disabled on the command line with -s.
$ python -s site_enable_user_site.py
在路径被添加到import path的过程中，path configuration file被扫描解析。
A path configuration file is a plain text file with the extension .pth.
每一行可以是：
路径配置文件的作用:
"Path configuration files can be used to extend the import path to look in locations that
would not have been added automatically. " Ref[2]
Demo-3: 没有使用路径配置文件的Case
创建一个目录with_modules。
$(ROOT_DIR)
｜－－ site_addsitedir.py
｜
｜－－with_modules
｜－－mymodule.py
site_addsitedir.py:
mymodule.py: mymodule.py
$ python site_addsitedir.py with_modules
"If the directory given to addsitedir() includes any files matching the pattern *.pth,
they are loaded as path configuration files." Ref[2]
Demo-4: 使用路径配置文件的Case
$(ROOT_DIR)
｜－－ site_addsitedir.py
｜
｜－－with_modules
｜－－pymotw.pth
｜－－subdir
|－－mymodule.py
pymotw.pth的内容是:
1 # Add a single subdirectory to the path. 2 ./subdir
运行 "$ python site_addsitedir.py with_modules" 的输出如下:
__file__: site_addsitedir.py cwd: /Users/XiaoKL/Projects/PrivateProject/PythonProject/site basename: site_addsitedir.py abspath: /Users/XiaoKL/Projects/PrivateProject/PythonProject/site/site_addsitedir.py script_directory: /Users/XiaoKL/Projects/PrivateProject/PythonProject/site module_directory: with_modules Could not import mymodule: No module named mymodule ------------ New paths: /Users/XiaoKL/Projects/PrivateProject/PythonProject/site/with_modules /Users/XiaoKL/Projects/PrivateProject/PythonProject/site/with_modules/subdir ------------- Loaded mymodule from with_modules/subdir/mymodule.py
"The site module is also responsible for loading site-wide customization defined by the local
site owner in a sitecustomize module.
Uses for sitecustomize include extending the import path and enabling coverage, profiling, or
other development tools." Ref[2]
Demo-5: sitecustomize的使用
创建 sitecustomize.py 如下：
1 print ‘Loading sitecustomize.py‘ 2 3 import site 4 import platform 5 import os 6 import sys 7 8 path = os.path.join(‘/opt‘, ‘python‘, sys.version[:3], platform.platform()) 9 print ‘Adding new path‘, path 10 11 site.addsitedir(path)
创建 site_sitecustomize.py 如下：
1 import sys 2 3 print ‘Running main program‘ 4 5 print ‘End of path:‘, sys.path[-1]
将脚本 sitecustomize.py 和 site_sitecustomize.py 都放在with_sitecustomize目录中：
with_sitecustomize/
|－－sitecustomize.py
|－－site_sitecustomize.py
然后执行如下命令：
1 $ PYTHONPATH=with_sitecustomize python with_sitecustomize/site_sitecustomize.py
输出如下：
Loading sitecustomize.py Adding new path /opt/python/2.7/Darwin-13.4.0-x86_64-i386-64bit Running main program End of path: /opt/python/2.7/Darwin-13.4.0-x86_64-i386-64bit
"Since sitecustomize.py is meant for system-wide configuration, it should be installed somewere
in the default path (usally in the site-packages directory). This example sets PYTHONPATH explicitly
to ensure the module is picked up." Ref[2]
Q: PYTHONPATH 是个什么东西?
"The import search path list can be modified before starting the interpreter by setting
the shell variable PYTHONPATH to a colon-separated list of directories."
"Similar to sitecustomize, the usercustomize module can be used to set up user-specific settings
each time the interpreter starts up. usercustomize is loaded after sitecustomize, so site-wide
customizations can be overridden." Ref[2]
"When the user site directory feature is disabled, usercustomize is not imported" Ref[2]
-S: Disable the import of the module site and the site-dependent manipulations of sys.path that it entails.
$ python -S site_import_path.py
1. site — Site-specific configuration hook
https://docs.python.org/2/library/site.html
2. site
http://pymotw.com/2/site/
3. site.py source code
https://hg.python.org/cpython/file/2.7/Lib/site.py
4. sys-prefix & sys-exec_prefix
http://pymotw.com/2/sys/interpreter.html#sys-prefix
Running code at Python startup
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原文地址：http://www.cnblogs.com/cwgk/p/4564557.html
