# `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.

A path configuration file is a file whose name has the form `name.pth` and exists in one of the four directories mentioned above; its contents are additional items (one per line) to be added to `sys.path`. Non-existing items 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. Lines starting with `import` (followed by space or tab) are executed.

备注

An executable line in a `.pth` file is run at every Python startup, regardless of whether a particular module is actually going to be used. Its impact should thus be kept to a minimum. The primary intended purpose of executable lines is to make the corresponding module(s) importable (load 3rd-party import hooks, adjust `PATH` etc). Any other initialization is supposed to be done upon a module's actual import, if and when it happens. Limiting a code chunk to a single line is a deliberate measure to discourage putting anything more complex here.

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。

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 subsubdirectories, `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。

## `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)

  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。

  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

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