# `site` --- サイト固有の設定フック

ソースコード: Lib/site.py

このモジュールは初期化中に自動的にインポートされます。 自動インポートはインタプリタの `-S` オプションで禁止できます。

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.

バージョン 3.3 で変更: 以前は `-S` を使っているときでも、モジュールをインポートするとパス変更が起動されていました。

It starts by constructing up to four directories from a head and a tail part. For the head part, it uses `sys.prefix` and `sys.exec_prefix`; empty heads are skipped. For the tail part, it uses the empty string and then `lib/site-packages` (on Windows) or `lib/pythonX.Y[t]/site-packages` (on Unix and macOS). (The optional suffix "t" indicates the free-threaded build, and is appended if `"t"` is present in the `sys.abiflags` constant.) For each of the distinct head-tail combinations, it sees if it refers to an existing directory, and if so, adds it to `sys.path` and also inspects the newly added path for configuration files.

バージョン 3.5 で変更: "site-python" ディレクトリのサポートは削除されました。

バージョン 3.13 で変更: On Unix, Free threading Python installations are identified by the "t" suffix in the version-specific directory name, such as `lib/python3.13t/`.

バージョン 3.14 で変更: `site` is no longer responsible for updating `sys.prefix` and `sys.exec_prefix` on Virtual Environments. This is now done during the path initialization. As a result, under Virtual Environments, `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()`.

バージョン 3.13 で変更: `.pth` ファイルは、最初に UTF-8 で、失敗した場合は locale encoding でデコードされるようになります。

バージョン 3.15 で変更: `.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.

バージョン 3.15 で非推奨、バージョン 3.20 で削除予定: 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.

注釈

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.

注釈

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.

注釈

`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 package configuration

    foo
    bar
    bletch

また、 `bar.pth` には:

    # bar package configuration

    bar

が記載されているとします。そのとき、次のバージョンごとのディレクトリが `sys.path` へこの順番で追加されます:

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

`bletch` は存在しないため省略されるということに注意してください。 `bar` ディレクトリは `foo` ディレクトリの前に来ます。なぜなら、 `bar.pth` がアルファベット順で `foo.pth` の前に来るからです。また、 `spam` はどちらのパス設定ファイルにも記載されていないため、省略されます。

Let's say that there is also a `foo.start` file containing the following:

    # foo package startup code

    foo.submod:initialize

Now, after `sys.path` has been extended as above, and before Python turns control over to user code, the `foo.submod` module is imported and the `initialize()` function from that module is called.

## Migrating from `import` lines in `.pth` files to `.start` files

If your package currently ships a `name.pth` file, you can keep all `sys.path` extension lines unchanged. Only `import` lines need to be migrated.

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 の設定

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.

バージョン 3.4 で変更: rlcompleter とhistory のアクティベーションが自動で行われるようになりました。

## モジュールの内容

site.PREFIXES

  siteパッケージディレクトリのprefixのリスト。

site.ENABLE_USER_SITE

  ユーザサイトディレクトリのステータスを示すフラグ。 `True` の場合、ユーザサイトディレクトリが有効で `sys.path` に追加されていることを意味しています。 `False` の場合、ユーザによるリクエスト(オプション `-s` か `PYTHONNOUSERSITE`)によって、 `None` の場合セキュリティ上の理由(ユーザまたはグループIDと実効IDの間のミスマッチ)あるいは管理者によって、ユーザサイトディレクトリが無効になっていることを示しています。

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/pythonX.Y[t]/site-packages` for UNIX and non-framework macOS builds, `~/Library/Python/X.Y/lib/python/site-packages` for macOS framework builds, and `%APPDATA%\Python\PythonXY\site-packages` on Windows. The optional "t" indicates the free-threaded build. This directory is a site directory, which means that `.pth` files in it will be processed.

site.USER_BASE

  ユーザの site-packages のベースとなるディレクトリへのパスです。 `getuserbase()` がまだ呼び出されていなければ `None` かもしれません。デフォルト値は UNIX と frameworkなしの macOS ビルドでは `~/.local` 、macOS framework ビルドでは `~/Library/Python/X.Y` 、Windows では `%APPDATA%\Python` です。この値は、スクリプト、データファイル、Python モジュールなどのインストール先のディレクトリを ユーザーインストールスキーム で計算するのに使われます。 `PYTHONUSERBASE` も参照してください。

site.main()

  モジュール検索パスに標準のサイト固有ディレクトリを追加します。この関数は、Python インタプリタが `-S` で開始されていない限り、このモジュールインポート時に自動的に呼び出されます。

  バージョン 3.3 で変更: この関数は以前は無条件に呼び出されていました。

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).

  バージョン 3.15 で変更: 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()

  全てのグローバルな site-packages ディレクトリのリストを返します。

  Added in version 3.2.

site.getuserbase()

  ユーザのベースディレクトリへのパス `USER_BASE` を返します。未初期化であればこの関数は `PYTHONUSERBASE` を参考にして、設定もします。

  Added in version 3.2.

site.getusersitepackages()

  ユーザ固有の site パッケージのディレクトリへのパス `USER_SITE` を返します。未初期化であればこの関数は `USER_BASE` を参考にして、設定もします。 ユーザ固有の site パッケージが `sys.path` に追加されたかどうかを確認するには `ENABLE_USER_SITE` を使ってください。

  Added in version 3.2.

## コマンドライン・インターフェース

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

引数なしで呼び出された場合、`sys.path` の中身を表示し、続けて `USER_BASE` とそのディレクトリが存在するかどうか、 `USER_SITE` とそのディレクトリが存在するかどうか、最後に `ENABLE_USER_SITE` の値を、標準出力に出力します。

--user-base

  ユーザのベースディレクトリを表示します。

--user-site

  ユーザの site-packages ディレクトリを表示します。

両方のオプションが指定された場合、ユーザのベースとユーザの site が(常にこの順序で) `os.pathsep` 区切りで表示されます。

いずれかのオプションが与えられた場合に、このスクリプトは次のいずれかの終了コードで終了します: ユーザの site-packages が有効ならば `0` 、ユーザにより無効にされていれば `1` 、セキュリティ的な理由あるいは管理者によって無効にされている場合 `2` 、そして何かエラーがあった場合は 2 より大きな値。

参考

- PEP 370 -- ユーザごとの `site-packages` ディレクトリ

- PEP 829 -- Startup entry points and the deprecation of import lines in `.pth` files

- sys.path モジュール検索パスの初期化 -- `sys.path`. の初期化。