Python.Module.site

Posted 2020-08-01 XiaoKL

site

" 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]

1. Import Path 

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

 

2. User Directories (用户目录)

http://pymotw.com/2/site/

2.1 USER_BASE 和 USER_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]

 

 

2.2 Disable user directory

The user directory can also be explicitly disabled on the command line with -s.

$ python -s site_enable_user_site.py

 

3. Path Configuration Files (路径配置文件)

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：

1. A full or relative path to another location that should be added to the import path.
2. A Python statement to be executed. All such lines must begin with an import statement.
3. Blank lines are ignored.
4. A line starting with # is treated as a comment and ignored.

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: 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

 

4. sitecustomize

"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."

 

5. usercustomize 

"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]

 

6. Disabling site

-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

 

 

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Reference

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

 

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TODO

Running code at Python startup

Modules and Imports

setuptools