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/pythonX.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/pythonX.Y. Suppose this has a subdirectory /usr/local/lib/pythonX.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/pythonX.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\PythonXY\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