site —— 指定域的配置钩子

源代码: Lib/site.py

这个模块将在初始化时被自动导入。 此自动导入可以通过使用解释器的 -S 选项来屏蔽。

导入此模块将会附加域特定的路径到模块搜索路径并且添加一些内建对象，除非使用了 -S 选项。在此例中，模块可以被安全地导入，而不会对模块搜索路径和内建对象有自动的修改或添加。要明确地触发通常域特定的添加，调用函数 site.main()。

在 3.3 版更改: 即便使用了 -S，也会导入此模块用于触发路径操纵。

它会从头部和尾部构建至多四个目录作为起点。 对于头部，它会使用 sys.prefix 和 sys.exec_prefix；空的头部会被跳过。 对于尾部，它会使用空字符串然后是 lib/site-packages (在 Windows 上) 或 lib/python*X.Y*/site-packages (在 Unix 和 Macintosh 上)。 对于每个不同的头-尾组合，它会查看其是否指向现有的目录，如果是的话，则将其添加到 sys.path 并且检查新添加目录中的配置文件。

在 3.5 版更改: 对 “site-python” 目录的支持已被移除。

如果名为 “pyvenv.cfg” 的文件存在于 sys.executable 之上的一个目录中，则 sys.prefix 和 sys.exec_prefix 将被设置为该目录，并且还会检查 site-packages （ sys.base_prefix 和 sys.base_exec_prefix 始终是 Python 安装的 “真实” 前缀）。 如果 “pyvenv.cfg” （引导程序配置文件）包含设置为非 “true”（不区分大小写）的 “include-system-site-packages” 键，则不会在系统级前缀中搜索 site-packages；反之则会。

一个路径配置文件是具有 *name*.pth 命名格式的文件，并且存在上面提到的四个目录之一中；它的内容是要添加到 sys.path 中的额外项目（每行一个）。不存在的项目不会添加到 sys.path，并且不会检查项目指向的是目录还是文件。项目不会被添加到 sys.path 超过一次。空行和由 # 起始的行会被跳过。以 import 开始的行（跟着空格或 TAB）会被执行。

注解

每次启动 Python，在 .pth 文件中的可执行行都将会被运行，而不管特定的模块实际上是否需要被使用。 因此，其影响应降至最低。可执行行的主要预期目的是使相关模块可导入（加载第三方导入钩子，调整 PATH 等）。如果它发生了，任何其他的初始化都应当在模块实际导入之前完成。将代码块限制为一行是一种有意采取的措施，不鼓励在此处放置更复杂的内容。

例如，假设 sys.prefix 和 sys.exec_prefix 已经被设置为 /usr/local。 Python X.Y 的库之后被安装为 /usr/local/lib/python*X.Y*。假设有一个拥有三个孙目录 foo, bar 和 spam 的子目录 /usr/local/lib/python*X.Y*/site-packages，并且有两个路径配置文件 foot.pth 和 bar.pth。假定 foo.pth 内容如下:

  1. # foo package configuration
  3. foo
  4. bar
  5. bletch

并且 bar.pth 包含:

  1. # bar package configuration
  3. bar

则下面特定版目录将以如下顺序被添加到 sys.path。

  1. /usr/local/lib/pythonX.Y/site-packages/bar
  2. /usr/local/lib/pythonX.Y/site-packages/foo

请注意 bletch 已被省略因为它并不存在；bar 目前在 foo 目录之前因为 bar.pth 按字母顺序排在 foo.pth 之前；而 spam 已被省略因为它在两个路径配置文件中都未被提及。

After these path manipulations, an attempt is made to import a module named sitecustomize, which can perform arbitrary site-specific customizations. It is typically created by a system administrator in the site-packages directory. If this import fails with an ImportError or its subclass exception, and the exception’s name attribute equals to 'sitecustomize', it is silently ignored. If Python is started without output streams available, as with pythonw.exe on Windows (which is used by default to start IDLE), attempted output from sitecustomize is ignored. Any other exception causes a silent and perhaps mysterious failure of the process.

After this, an attempt is made to import a module named usercustomize, which can perform arbitrary user-specific customizations, if ENABLE_USER_SITE is true. This file is intended to be created in the user site-packages directory (see below), which is part of sys.path unless disabled by -s. If this import fails with an ImportError or its subclass exception, and the exception’s name attribute equals to 'usercustomize', it is silently ignored.

Note that for some non-Unix systems, sys.prefix and sys.exec_prefix are empty, and the path manipulations are skipped; however the import of sitecustomize and usercustomize is still attempted.

Readline 配置

On systems that support readline, this module will also import and configure the rlcompleter module, if Python is started in interactive mode and without the -S option. The default behavior is enable tab-completion and to use ~/.python_history as the history save file. To disable it, delete (or override) the sys.__interactivehook__ attribute in your sitecustomize or usercustomize module or your PYTHONSTARTUP file.

在 3.4 版更改: Activation of rlcompleter and history was made automatic.

模块内容

site.PREFIXES

site-packages 目录的前缀列表。

site.ENABLE_USER_SITE

Flag showing the status of the user site-packages directory. True means that it is enabled and was added to sys.path. False means that it was disabled by user request (with -s or PYTHONNOUSERSITE). None means it was disabled for security reasons (mismatch between user or group id and effective id) or by an administrator.

site.USER_SITE

Path to the user site-packages for the running Python. Can be None if getusersitepackages() hasn’t been called yet. Default value is ~/.local/lib/python*X.Y*/site-packages for UNIX and non-framework Mac OS X builds, ~/Library/Python/*X.Y*/lib/python/site-packages for Mac framework builds, and *%APPDATA%*\Python\Python*XY*\site-packages on Windows. This directory is a site directory, which means that .pth files in it will be processed.

site.USER_BASE

Path to the base directory for the user site-packages. Can be None if getuserbase() hasn’t been called yet. Default value is ~/.local for UNIX and Mac OS X non-framework builds, ~/Library/Python/*X.Y* for Mac framework builds, and *%APPDATA%*\Python for Windows. This value is used by Distutils to compute the installation directories for scripts, data files, Python modules, etc. for the user installation scheme. See also PYTHONUSERBASE.

site.main()

Adds all the standard site-specific directories to the module search path. This function is called automatically when this module is imported, unless the Python interpreter was started with the -S flag.

在 3.3 版更改: 这个函数使用无条件调用。

site.addsitedir(sitedir, known_paths=None)

Add a directory to sys.path and process its .pth files. Typically used in sitecustomize or usercustomize (see above).

site.getsitepackages()

返回包含所有全局 site-packages 目录的列表。

3.2 新版功能.

site.getuserbase()

Return the path of the user base directory, USER_BASE. If it is not initialized yet, this function will also set it, respecting PYTHONUSERBASE.

3.2 新版功能.

site.getusersitepackages()

Return the path of the user-specific site-packages directory, USER_SITE. If it is not initialized yet, this function will also set it, respecting USER_BASE. To determine if the user-specific site-packages was added to sys.path ENABLE_USER_SITE should be used.

3.2 新版功能.

命令行界面

site 模块还提供了一个从命令行获取用户目录的方式:

  1. $ python3 -m site --user-site
  2. /home/user/.local/lib/python3.3/site-packages

If it is called without arguments, it will print the contents of sys.path on the standard output, followed by the value of USER_BASE and whether the directory exists, then the same thing for USER_SITE, and finally the value of ENABLE_USER_SITE.

--user-base

输出用户基本的路径。

--user-site

输出用户site-packages目录的路径。

If both options are given, user base and user site will be printed (always in this order), separated by os.pathsep.

If any option is given, the script will exit with one of these values: 0 if the user site-packages directory is enabled, 1 if it was disabled by the user, 2 if it is disabled for security reasons or by an administrator, and a value greater than 2 if there is an error.

参见

PEP 370 — 分用户的 site-packages 目录