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:
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
, ordbm.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 existthe empty string (
''
) if the file's format can't be guesseda 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 thesetdefault()
method requires two arguments. It also supports a "closing" context manager via thewith
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 3.15.0a0 (unreleased).
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
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.
This module is not supported on mobile platforms or WebAssembly platforms.
- exception dbm.gnu.error¶
I/O エラーのような
dbm.gnu
特有のエラーで送出されます。誤ったキーの指定のように、一般的なマップ型のエラーに対してはKeyError
が送出されます。
- 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.'m'
: Do not use mmap(2). This may harm performance, but improve crash tolerance. .. versionadded:: next
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 methodsitems()
,values()
,pop()
,popitem()
, andupdate()
are not supported, thekeys()
method returns a list, and thesetdefault()
method requires two arguments. It also supports a "closing" context manager via thewith
keyword.バージョン 3.2 で変更: Added the
get()
andsetdefault()
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 library.
This module can be used with the "classic" NDBM interface or the
GDBM 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.
This module is not supported on mobile platforms or WebAssembly platforms.
- exception dbm.ndbm.error¶
I/O エラーのような
dbm.ndbm
特有のエラーで送出されます。誤ったキーの指定のように、一般的なマップ型のエラーに対してはKeyError
が送出されます。
- 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 methodsitems()
,values()
,pop()
,popitem()
, andupdate()
are not supported, thekeys()
method returns a list, and thesetdefault()
method requires two arguments. It also supports a "closing" context manager via thewith
keyword.バージョン 3.2 で変更: Added the
get()
andsetdefault()
methods.バージョン 3.13 で変更: Added the
clear()
method.The following method is also provided:
- ndbm.close()¶
Close the NDBM database.
dbm.dumb
--- 可搬性のある DBM 実装¶
ソースコード: Lib/dbm/dumb.py
注釈
dbm.dumb
モジュールは、 dbm
が頑健なモジュールを他に見つけることができなかった際の最後の手段とされています。 dbm.dumb
モジュールは速度を重視して書かれているわけではなく、他のデータベースモジュールのように重い使い方をするためのものではありません。
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¶
I/O エラーのような
dbm.dumb
特有のエラーの際に送出されます。不正なキーを指定したときのような、一般的な対応付けエラーの際にはKeyError
が送出されます。
- 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()
anditems()
methods return lists, and thesetdefault()
method requires two arguments. It also supports a "closing" context manager via thewith
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 3.15.0a0 (unreleased).
- dumbdbm.sync()¶
Synchronize the on-disk directory and data files. This method is called by the
shelve.Shelf.sync()
method.