"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/python*X.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/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 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/python*X.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\Python*XY*\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。
