"site" --- 站点专属的配置钩子
*****************************

**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。

Importing this module normally appends site-specific paths to the
module search path and adds callables, including "help()" to the
built-in namespace. However, Python startup option "-S" blocks this,
and this module can be safely imported with no automatic modifications
to the module search path or additions to the builtins.  To explicitly
trigger the usual site-specific additions, call the "main()" function.

在 3.3 版本发生变更: 在之前即便使用了 "-S"，导入此模块仍然会触发路径操
纵。

它会以一个头部和一个尾部来构造至多四个目录作为起点。对于头部，它将使用
"sys.prefix" 和 "sys.exec_prefix"；空的头部会被跳过。对于尾部，它将使
用空字符串然后是 "lib/site-packages" (在 Windows 上) 或
"lib/python*X.Y[t]*/site-packages" (在 Unix 和 macOS 上)。 (可选后缀
"t" 表示 *free-threaded build*，并会在 ""t"" 存在于 "sys.abiflags" 常
量中时被添加。) 对于每个不同的头部 - 尾部组合，它会查看其是否指向现有
的目录，如果确实如此，则将其添加到 "sys.path" 并且还会检查新添加目录中
的配置文件。

在 3.5 版本发生变更: 对 "site-python" 目录的支持已被移除。

在 3.13 版本发生变更: 在 Unix 上，*自由线程* Python 安装版是在版本专属
的目录名称中以 "t" 后缀来标识的，例如 "lib/python3.13t/"。

在 3.14 版本发生变更: "site" is no longer responsible for updating
"sys.prefix" and "sys.exec_prefix" on 虚拟环境. This is now done
during the path initialization. As a result, under 虚拟环境,
"sys.prefix" and "sys.exec_prefix" no longer depend on the "site"
initialization, and are therefore unaffected by "-S".

When running under a virtual environment, the "pyvenv.cfg" file in
"sys.prefix" is checked for site-specific configurations. If the
"include-system-site-packages" key exists and is set to "true" (case-
insensitive), the system-level prefixes will be searched for site-
packages, otherwise they won't.  If the system-level prefixes are not
searched then the user site prefixes are also implicitly not searched
for site-packages.

The "site" module recognizes two startup configuration files of the
form "*name*.pth" for path configurations, and "*name*.start" for pre-
first-line code execution.  Both files can exist in one of the four
directories mentioned above.  Within each directory, these files are
sorted alphabetically by filename, then parsed in sorted order.


Path extensions (".pth" files)
==============================

"*name*.pth" contains additional items (one per line) to be appended
to "sys.path".  Items that name non-existing directories are never
added to "sys.path", and no check is made that the item refers to a
directory rather than a file.  No item is added to "sys.path" more
than once.  Blank lines and lines beginning with "#" are skipped.

For backward compatibility, lines starting with "import" (followed by
space or tab) are executed with "exec()".

在 3.13 版本发生变更: 现在 ".pth" 文件会首先使用 UTF-8 来解码，如果失
败会再改用 *locale encoding* 来解码。

在 3.15 版本发生变更: ".pth" file lines starting with "import" are
deprecated.  During the deprecation period, such lines are still
executed (except in the case below), but a diagnostic message is
emitted only when the "-v" flag is given."import" lines in
"*name*.pth" are silently ignored when a matching "*name*.start" file
exists.Errors on individual lines no longer abort processing of the
rest of the file.  Each error is reported and the remaining lines
continue to be processed.

从 3.15 版起已弃用，将在 3.20 版中移除: Decoding "*name*.pth" files in
any encoding other than "utf-8-sig" is deprecated in Python 3.15, and
support for decoding from the locale encoding will be removed in
Python 3.20."import" lines in "*name*.pth" files are deprecated and
will be silently ignored in Python 3.18 and 3.19.  In Python 3.20 a
warning will be produced for "import" lines in "*name*.pth" files.


Startup entry points (".start" files)
=====================================

Added in version 3.15.

A startup entry point file is a file whose name has the form
"*name*.start" and exists in one of the site-packages directories
described above.  Each file specifies entry points to be called during
interpreter startup, using the "pkg.mod:callable" syntax understood by
"pkgutil.resolve_name()".

Each non-blank line that does not begin with "#" must contain an entry
point reference in the form "pkg.mod:callable".  The colon and
callable portion are mandatory.  Each callable is invoked with no
arguments, and any return value is discarded.

".start" files are processed after all ".pth" path extensions have
been applied to "sys.path", ensuring that paths are available before
any startup code runs.

Unlike "sys.path" extensions from ".pth" files, duplicate entry points
are **not** de-duplicated --- if an entry point appears more than
once, it will be called more than once.

If an exception occurs during resolution or invocation of an entry
point, a traceback is printed to "sys.stderr" and processing continues
with the remaining entry points.

".start" files must be encoded in UTF-8.

**PEP 829** defined the original specification for these features.

备注:

  If a "*name*.start" file exists alongside a "*name*.pth" file with
  the same base name, any "import" lines in the ".pth" file are
  ignored in favor of the entry points in the ".start" file.

备注:

  Executable lines ("import" lines in "*name*.pth" files and
  "*name*.start" file entry points) are always run at Python startup
  (unless "-S" is given to disable the "site.py" module entirely),
  regardless of whether a particular module is actually going to be
  used.

备注:

  "*name*.start" files invoke "pkgutil.resolve_name()" with
  "strict=True", which requires the full "pkg.mod:callable" form.


Startup file examples
=====================

For example, suppose "sys.prefix" and "sys.exec_prefix" are set to
"/usr/local".  The Python X.Y library is then installed in
"/usr/local/lib/python*X.Y*".  Suppose this has a subdirectory
"/usr/local/lib/python*X.Y*/site-packages" with three sub-
subdirectories, "foo", "bar" and "spam", and two path configuration
files, "foo.pth" and "bar.pth".  Assume "foo.pth" contains the
following:

   # foo 包配置

   foo
   bar
   bletch

并且 "bar.pth" 包含:

   # bar 包配置

   bar

则下面特定版本目录将以如下顺序被添加到 "sys.path":

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

请注意 "bletch" 已被省略因为它并不存在；"bar" 目录在 "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。

让我们假设还有一个 "foo.start" 文件包含以下内容:

   # foo 包启动代码

   foo.submod:initialize

现在，当 "sys.path" 像上面那样扩展之后，并在 Python 将控制权交给用户代
码之前，"foo.submod" 模块将被导入且该模块的 "initialize()" 函数将被调
用。


将 ".pth" 文件中的 "import" 行迁移至 ".start" 文件
==================================================

如果你的包目前带有 "*name*.pth" 文件，你可以保持所有 "sys.path" 扩展行
不变。 只有 "import" 行需要迁移。

To migrate, create a callable (taking zero arguments) within an
importable module in your package.  Reference it as a
"pkg.mod:callable" entry point in a matching "*name*.start" file.
Move everything on your "import" line after the first semi-colon into
the "callable()" function.

If your package must straddle older Pythons that do not support **PEP
829** and newer Pythons that do, change the "import" lines in your
"*name*.pth" to use the following form:

   import pkg.mod; pkg.mod.callable()

Older Pythons will execute these "import" lines, while newer Pythons
will ignore them in favor of the "*name*.start" file.  After the
straddling period, remove all "import" lines from your ".pth" files.


"sitecustomize"
===============

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 "'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.


"usercustomize"
===============

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 "'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
to 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 版本发生变更: rlcompleter 和 history 会被自动激活。


模块内容
========

site.PREFIXES

   site-packages 目录的前缀列表。

site.ENABLE_USER_SITE

   显示用户 site-packages 目录状态的旗标。"True" 意味着它被启用并被添
   加到 "sys.path"。"False" 意味着它按照用户请求被禁用 (通过 "-s" 或
   "PYTHONNOUSERSITE")。"None" 意味着它因安全理由（user 或 group id 和
   effective id 之间不匹配）或是被管理员所禁用。

site.USER_SITE

   运行中的 Python 的用户级 site-packages 的路径。它可以为 "None"，如
   果 "getusersitepackages()" 尚未被调用的话。默认值在 UNIX 和 macOS
   非框架构建版上为 "~/.local/lib/python*X.Y*[t]/site-packages"，在
   macOS 框架构建版上为 "~/Library/Python/*X.Y*/lib/python/site-
   packages"，而在 Windows 上为 "*%APPDATA%*\Python\Python*XY*\site-
   packages"。可选的 "t" 表示自由线程构建版。此目录属于 site 目录，这
   意味着其中的 ".pth" 文件将会被处理。

site.USER_BASE

   用户级 site-packages 的基准目录的路径。如果尚未调用 "getuserbase()"
   则它可以为 "None"。默认值在 Unix 和 macOS 非框架编译版上为
   "~/.local"，在 macOS 框架编译版上为 "~/Library/Python/*X.Y*"，而在
   Windows 上则为 "*%APPDATA%*\Python"。 这个值会被用于计算针对 用户安
   装方案 的脚本、数据文件、Python 模块等的安装目录。 另请参阅
   "PYTHONUSERBASE"。

site.main()

   将所有的标准站点专属目录添加到模块搜索路径。这个函数会在导入此模块
   时被自动调用，除非 Python 解释器启动时附带了 "-S" 旗标。

   在 3.3 版本发生变更: 这个函数曾会被无条件调用。

site.addsitedir(sitedir, known_paths=None, *, defer_processing_start_files=False)

   Add a directory to sys.path and parse the ".pth" and ".start" files
   found in that directory.  Typically used in "sitecustomize" or
   "usercustomize" (see above).

   The *known_paths* argument is an optional set of case-normalized
   paths used to prevent duplicate "sys.path" entries.  When "None"
   (the default), the set is built from the current "sys.path".

   While ".pth" and ".start" files are always parsed, set
   *defer_processing_start_files* to "True" to prevent processing the
   startup data found in those files, so that you can process them
   explicitly (this is typically used by the "main()" function).

   在 3.15 版本发生变更: Also processes ".start" files.  See Startup
   entry points (.start files). All ".pth" and ".start" files are now
   read and accumulated before any path extensions, "import" line
   execution, or entry point invocations take place.

site.getsitepackages()

   返回包含所有全局 site-packages 目录的列表。

   Added in version 3.2.

site.getuserbase()

   返回用户基准目录的路径 "USER_BASE"。如果它尚未被初始化，则此函数还
   将参照 "PYTHONUSERBASE" 来设置它。

   Added in version 3.2.

site.getusersitepackages()

   返回用户专属 site-packages 目录的路径 "USER_SITE"。如果它尚未被初始
   化，则此函数还将参照 "USER_BASE" 来设置它。要确定用户专属 site-
   packages 是否已被添加到 "sys.path" 则应当使用 "ENABLE_USER_SITE".

   Added in version 3.2.


命令行接口
==========

The "site" module also provides a way to get the user directories from
the command line:

   $ python -m site --user-site
   /home/user/.local/lib/python3.11/site-packages

如果它被不带参数地调用，它将在标准输出打印 "sys.path" 的内容，再打印
"USER_BASE" 的值以及该目录是否存在，然后打印 "USER_SITE" 的相应信息，
最后打印 "ENABLE_USER_SITE" 的值。

--user-base

   输出用户基准目录的路径。

--user-site

   输出用户 site-packages 目录的路径。

如果同时给出了两个选项，则将打印用户基准目录和用户站点信息（总是按此顺
序），并以 "os.pathsep" 分隔。

如果给出了其中一个选项，脚本将退出并返回以下值中的一个：如果用户级
site-packages 目录被启用则为 "0"，如果它被用户禁用则为 "1"，如果它因安
全理由或被管理员禁用则为 "2"，如果发生错误则为大于 2 的值。

参见:

  * **PEP 370** -- 分用户的 site-packages 目录

  * **PEP 829** -- 启动入口点与 ".pth" 文件中导入行的弃用

  * sys.path 模块搜索路径的初始化 -- "sys.path" 的初始化。
