"dbm" --- Unix "データベース" へのインターフェース
**************************************************

**ソースコード:** Lib/dbm/__init__.py

======================================================================

"dbm" is a generic interface to variants of the DBM database:

* "dbm.sqlite3"

* "dbm.gnu"

* "dbm.ndbm"

If none of these modules are installed, the slow-but-simple
implementation in module "dbm.dumb" will be used. There is a third
party interface to the Oracle Berkeley DB.

注釈:

  None of the underlying modules will automatically shrink the disk
  space used by the database file. However, "dbm.sqlite3", "dbm.gnu"
  and "dbm.dumb" provide a "reorganize()" method that can be used for
  this purpose.

exception dbm.error

   サポートされているモジュールそれぞれによって送出される可能性のある
   例外を含むタプル。これにはユニークな例外があり、最初の要素として同
   じく "dbm.error" という名前の例外が含まれます --- "dbm.error" が送
   出される場合、後者(訳注:タプルの "dbm.error" ではなく例外
   "dbm.error")が使用されます。

dbm.whichdb(filename)

   This function attempts to guess which of the several simple
   database modules available --- "dbm.sqlite3", "dbm.gnu",
   "dbm.ndbm", or "dbm.dumb" --- should be used to open a given file.

   Return one of the following values:

   * "None" if the file can't be opened because it's unreadable or
     doesn't exist

   * the empty string ("''") if the file's format can't be guessed

   * a string containing the required module name, such as
     "'dbm.ndbm'" or "'dbm.gnu'"

   バージョン 3.11 で変更: *filename* accepts a *path-like object*.

dbm.open(file, flag='r', mode=0o666)

   Open a database and return the corresponding database object.

   パラメータ:
      * **file** (*path-like object*) --

        The database file to open.

        If the database file already exists, the "whichdb()" function
        is used to determine its type and the appropriate module is
        used; if it does not exist, the first submodule listed above
        that can be imported is used.

      * **flag** (*str*) --

        * "'r'" (default): Open existing database for reading only.

        * "'w'": Open existing database for reading and writing.

        * "'c'": Open database for reading and writing, creating it if
          it doesn't exist.

        * "'n'": Always create a new, empty database, open for reading
          and writing.

      * **mode** (*int*) -- The Unix file access mode of the file
        (default: octal "0o666"), used only when the database has to
        be created.

   バージョン 3.11 で変更: *file* accepts a *path-like object*.

The object returned by "open()" supports the basic functionality of
mutable *mappings*; keys and their corresponding values can be stored,
retrieved, and deleted, and iteration, the "in" operator and methods
"keys()", "get()", "setdefault()" and "clear()" are available. The
"keys()" method returns a list instead of a view object. The
"setdefault()" method requires two arguments.

Key and values are always stored as "bytes". This means that when
strings are used they are implicitly converted to the default encoding
before being stored.

これらのオブジェクトは、 "with" 文での使用にも対応しています。with 文
を使用した場合、終了時に自動的に閉じられます。

バージョン 3.2 で変更: "get()" and "setdefault()" methods are now
available for all "dbm" backends.

バージョン 3.4 で変更: Added native support for the context management
protocol to the objects returned by "open()".

バージョン 3.8 で変更: Deleting a key from a read-only database raises
a database module specific exception instead of "KeyError".

バージョン 3.13 で変更: "clear()" methods are now available for all
"dbm" backends.

以下の例ではホスト名と対応するタイトルをいくつか記録し、データベースの
内容を出力します:

   import dbm

   # Open database, creating it if necessary.
   with dbm.open('cache', 'c') as db:

       # Record some values
       db[b'hello'] = b'there'
       db['www.python.org'] = 'Python Website'
       db['www.cnn.com'] = 'Cable News Network'

       # Note that the keys are considered bytes now.
       assert db[b'www.python.org'] == b'Python Website'
       # Notice how the value is now in bytes.
       assert db['www.cnn.com'] == b'Cable News Network'

       # Often-used methods of the dict interface work too.
       print(db.get('python.org', b'not present'))

       # Storing a non-string key or value will raise an exception (most
       # likely a TypeError).
       db['www.yahoo.com'] = 4

   # db is automatically closed when leaving the with statement.

参考:

  "shelve" モジュール
     非文字列データを記録する永続化モジュール。

個々のサブモジュールは以降の節で説明されます。


"dbm.sqlite3" --- SQLite backend for dbm
========================================

Added in version 3.13.

**Source code:** Lib/dbm/sqlite3.py

======================================================================

This module uses the standard library "sqlite3" module to provide an
SQLite backend for the "dbm" module. The files created by
"dbm.sqlite3" can thus be opened by "sqlite3", or any other SQLite
browser, including the SQLite CLI.

Availability: not WASI.

このモジュールは WebAssembly では動作しないか、利用不可です。詳しくは
、WebAssembly プラットフォーム を見てください。

dbm.sqlite3.open(filename, /, flag='r', mode=0o666)

   Open an SQLite database.

   パラメータ:
      * **filename** (*path-like object*) -- The path to the database
        to be opened.

      * **flag** (*str*) --

        * "'r'" (default): Open existing database for reading only.

        * "'w'": Open existing database for reading and writing.

        * "'c'": Open database for reading and writing, creating it if
          it doesn't exist.

        * "'n'": Always create a new, empty database, open for reading
          and writing.

      * **mode** -- The Unix file access mode of the file (default:
        octal "0o666"), used only when the database has to be created.

   The returned database object behaves similar to a mutable
   *mapping*, but the "keys()" method returns a list, and the
   "setdefault()" method requires two arguments. It also supports a
   "closing" context manager via the "with" keyword.

   The following methods are also provided:

   sqlite3.close()

      Close the SQLite database.

   sqlite3.reorganize()

      If you have carried out a lot of deletions and would like to
      shrink the space used on disk, this method will reorganize the
      database; otherwise, deleted file space will be kept and reused
      as new (key, value) pairs are added.

      注釈:

        While reorganizing, as much as two times the size of the
        original database is required in free disk space. However, be
        aware that this factor changes for each "dbm" submodule.

      Added in version 3.15.


"dbm.gnu" --- GNU database manager
==================================

**ソースコード:** Lib/dbm/gnu.py

======================================================================

The "dbm.gnu" module provides an interface to the GDBM (GNU dbm)
library, similar to the "dbm.ndbm" module, but with additional
functionality like crash tolerance.

注釈:

  The file formats created by "dbm.gnu" and "dbm.ndbm" are
  incompatible and can not be used interchangeably.

Availability: not Android, not iOS, not WASI.

このモジュールは モバイルプラットフォーム と WebAssemblyプラットフォー
ム をサポートしません。

Availability: Unix.

exception dbm.gnu.error

   Raised on "dbm.gnu"-specific errors, such as I/O errors. "KeyError"
   is raised for general mapping errors like specifying an incorrect
   key.

dbm.gnu.open_flags

   A string of characters the *flag* parameter of "open()" supports.

dbm.gnu.open(filename, flag='r', mode=0o666, /)

   Open a GDBM database and return a "gdbm" object.

   パラメータ:
      * **filename** (*path-like object*) -- The database file to
        open.

      * **flag** (*str*) --

        * "'r'" (default): Open existing database for reading only.

        * "'w'": Open existing database for reading and writing.

        * "'c'": Open database for reading and writing, creating it if
          it doesn't exist.

        * "'n'": Always create a new, empty database, open for reading
          and writing.

        The following additional characters may be appended to control
        how the database is opened:

        * "'f'": Open the database in fast mode. Writes to the
          database will not be synchronized.

        * "'s'": Synchronized mode. Changes to the database will be
          written immediately to the file.

        * "'u'": Do not lock database.

        Not all flags are valid for all versions of GDBM. See the
        "open_flags" member for a list of supported flag characters.

      * **mode** (*int*) -- The Unix file access mode of the file
        (default: octal "0o666"), used only when the database has to
        be created.

   例外:
      **error** -- If an invalid *flag* argument is passed.

   バージョン 3.11 で変更: *filename* accepts a *path-like object*.

   "gdbm" objects behave similar to mutable *mappings*, but methods
   "items()", "values()", "pop()", "popitem()", and "update()" are not
   supported, the "keys()" method returns a list, and the
   "setdefault()" method requires two arguments. It also supports a
   "closing" context manager via the "with" keyword.

   バージョン 3.2 で変更: Added the "get()" and "setdefault()"
   methods.

   バージョン 3.13 で変更: Added the "clear()" method.

   The following methods are also provided:

   gdbm.close()

      Close the GDBM database.

   gdbm.firstkey()

      It's possible to loop over every key in the database using this
      method  and the "nextkey()" method.  The traversal is ordered by
      GDBM's internal hash values, and won't be sorted by the key
      values.  This method returns the starting key.

   gdbm.nextkey(key)

      データベースの順方向探索において、*key* よりも後に来るキーを返し
      ます。以下のコードはデータベース "db" について、キー全てを含むリ
      ストをメモリ上に生成することなく全てのキーを出力します:

         k = db.firstkey()
         while k is not None:
             print(k)
             k = db.nextkey(k)

   gdbm.reorganize()

      If you have carried out a lot of deletions and would like to
      shrink the space used by the GDBM file, this routine will
      reorganize the database.  "gdbm" objects will not shorten the
      length of a database file except by using this reorganization;
      otherwise, deleted file space will be kept and reused as new
      (key, value) pairs are added.

      注釈:

        While reorganizing, as much as one time the size of the
        original database is required in free disk space. However, be
        aware that this factor changes for each "dbm" submodule.

   gdbm.sync()

      データベースが高速モードで開かれていた場合、このメソッドはディス
      クにまだ書き込まれていないデータを全て書き込ませます。


"dbm.ndbm" --- New Database Manager
===================================

**ソースコード:** Lib/dbm/ndbm.py

======================================================================

The "dbm.ndbm" module provides an interface to the NDBM (New Database
Manager) library. This module can be used with the "classic" NDBM
interface or the GDBM (GNU dbm) compatibility interface.

注釈:

  The file formats created by "dbm.gnu" and "dbm.ndbm" are
  incompatible and can not be used interchangeably.

警告:

  The NDBM library shipped as part of macOS has an undocumented
  limitation on the size of values, which can result in corrupted
  database files when storing values larger than this limit. Reading
  such corrupted files can result in a hard crash (segmentation
  fault).

Availability: not Android, not iOS, not WASI.

このモジュールは モバイルプラットフォーム と WebAssemblyプラットフォー
ム をサポートしません。

Availability: Unix.

exception dbm.ndbm.error

   Raised on "dbm.ndbm"-specific errors, such as I/O errors.
   "KeyError" is raised for general mapping errors like specifying an
   incorrect key.

dbm.ndbm.library

   Name of the NDBM implementation library used.

dbm.ndbm.open(filename, flag='r', mode=0o666, /)

   Open an NDBM database and return an "ndbm" object.

   パラメータ:
      * **filename** (*path-like object*) -- The basename of the
        database file (without the ".dir" or ".pag" extensions).

      * **flag** (*str*) --

        * "'r'" (default): Open existing database for reading only.

        * "'w'": Open existing database for reading and writing.

        * "'c'": Open database for reading and writing, creating it if
          it doesn't exist.

        * "'n'": Always create a new, empty database, open for reading
          and writing.

      * **mode** (*int*) -- The Unix file access mode of the file
        (default: octal "0o666"), used only when the database has to
        be created.

   バージョン 3.11 で変更: Accepts *path-like object* for filename.

   "ndbm" objects behave similar to mutable *mappings*, but methods
   "items()", "values()", "pop()", "popitem()", and "update()" are not
   supported, the "keys()" method returns a list, and the
   "setdefault()" method requires two arguments. It also supports a
   "closing" context manager via the "with" keyword.

   バージョン 3.2 で変更: Added the "get()" and "setdefault()"
   methods.

   バージョン 3.13 で変更: Added the "clear()" method.

   次のメソッドを提供しています:

   ndbm.close()

      Close the NDBM database.


"dbm.dumb" --- Portable DBM implementation
==========================================

**ソースコード:** Lib/dbm/dumb.py

注釈:

  The "dbm.dumb" module is intended as a last resort fallback for the
  "dbm" module when a more robust module is not available. The
  "dbm.dumb" module is not written for speed and is not nearly as
  heavily used as the other database modules.

======================================================================

The "dbm.dumb" module provides a persistent "dict"-like interface
which is written entirely in Python. Unlike other "dbm" backends, such
as "dbm.gnu", no external library is required.

The "dbm.dumb" module defines the following:

exception dbm.dumb.error

   Raised on "dbm.dumb"-specific errors, such as I/O errors.
   "KeyError" is raised for general mapping errors like specifying an
   incorrect key.

dbm.dumb.open(filename, flag='c', mode=0o666)

   Open a "dbm.dumb" database.

   パラメータ:
      * **filename** --

        The basename of the database file (without extensions). A new
        database creates the following files:

        * "*filename*.dat"

        * "*filename*.dir"

      * **flag** (*str*) --

        * "'r'": Open existing database for reading only.

        * "'w'": Open existing database for reading and writing.

        * "'c'" (default): Open database for reading and writing,
          creating it if it doesn't exist.

        * "'n'": Always create a new, empty database, open for reading
          and writing.

      * **mode** (*int*) -- The Unix file access mode of the file
        (default: octal "0o666"), used only when the database has to
        be created.

   警告:

     十分に大きかったり複雑だったりするエントリーのあるデータベースを
     読み込んでいるときに、 Python の抽象構文木コンパイラのスタックの
     深さの限界を越えるせいで、 Python インタプリタをクラッシュさせる
     ことができます。

   警告:

     "dbm.dumb" does not support concurrent read/write access.
     (Multiple simultaneous read accesses are safe.) When a program
     has the database open for writing, no other program should have
     it open for reading or writing.

   バージョン 3.5 で変更: "open()" always creates a new database when
   *flag* is "'n'".

   バージョン 3.8 で変更: A database opened read-only if *flag* is
   "'r'". A database is not created if it does not exist if *flag* is
   "'r'" or "'w'".

   バージョン 3.11 で変更: *filename* accepts a *path-like object*.

   The returned database object behaves similar to a mutable
   *mapping*, but the "keys()" and "items()" methods return lists, and
   the "setdefault()" method requires two arguments. It also supports
   a "closing" context manager via the "with" keyword.

   The following methods are also provided:

   dumbdbm.close()

      Close the database.

   dumbdbm.reorganize()

      If you have carried out a lot of deletions and would like to
      shrink the space used on disk, this method will reorganize the
      database; otherwise, deleted file space will not be reused.

      注釈:

        While reorganizing, no additional free disk space is required.
        However, be aware that this factor changes for each "dbm"
        submodule.

      Added in version 3.15.

   dumbdbm.sync()

      Synchronize the on-disk directory and data files.  This method
      is called by the "shelve.Shelf.sync()" method.
