dbm --- Unix "databases" 的介面

原始碼：Lib/dbm/__init__.py

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

If none of these modules are installed, theslow-but-simple implementation in moduledbm.dumb will be used. Thereis athird party interface tothe Oracle Berkeley DB.

exceptiondbm.error

A tuple containing the exceptions that can be raised by each of the supportedmodules, with a unique exception also nameddbm.error as the firstitem --- the latter is used whendbm.error is raised.

dbm.whichdb(filename)

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

回傳以下其中一個值：

  • 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'

在 3.11 版的變更:filename accepts apath-like object.

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

Open a database and return the corresponding database object.

參數:

  • file (path-like object) --

    要打開的資料庫檔案

    If the database file already exists, thewhichdb() function is used todetermine 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: octal0o666),used only when the database has to be created.

在 3.11 版的變更:file 接受一個類路徑物件。

The object returned byopen() supports the same basic functionality as adict; keys and their corresponding values can be stored, retrieved, anddeleted, and thein operator and thekeys() method areavailable, as well asget() andsetdefault() methods.

Key and values are always stored asbytes. This means that whenstrings are used they are implicitly converted to the default encoding beforebeing stored.

These objects also support being used in awith statement, whichwill automatically close them when done.

在 3.2 版的變更:get() andsetdefault() methods are now available for alldbm backends.

在 3.4 版的變更:Added native support for the context management protocol to the objectsreturned byopen().

在 3.8 版的變更:Deleting a key from a read-only database raises a database module specific exceptioninstead ofKeyError.

The following example records some hostnames and a corresponding title, andthen prints out the contents of the database:

importdbm# Open database, creating it if necessary.withdbm.open('cache','c')asdb:# Record some valuesdb[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.assertdb[b'www.python.org']==b'Python Website'# Notice how the value is now in bytes.assertdb['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.

也參考

shelve 模組

Persistence module which stores non-string data.

The individual submodules are described in the following sections.

dbm.sqlite3 --- SQLite backend for dbm

在 3.13 版被加入.

原始碼：Lib/dbm/sqlite3.py

This module uses the standard librarysqlite3 module to provide anSQLite backend for thedbm module.The files created bydbm.sqlite3 can thus be opened bysqlite3,or any other SQLite browser, including the SQLite CLI.

適用: not WASI.

此模組在 WebAssembly 平台上不起作用或無法使用。更多資訊請參閱WebAssembly 平台。

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

Open an SQLite database.The returned object behaves like amapping,implements aclose() method,and supports a "closing" context manager via thewith keyword.

參數:

  • filename (path-like object) -- 要打開的資料庫路徑

  • 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: octal0o666),used only when the database has to be created.

dbm.gnu --- GNU 資料庫管理器

原始碼：Lib/dbm/gnu.py

Thedbm.gnu module provides an interface to theGDBMlibrary, similar to thedbm.ndbm module, but with additionalfunctionality like crash tolerance.

備註

The file formats created bydbm.gnu anddbm.ndbm are incompatibleand can not be used interchangeably.

適用: not Android, not iOS, not WASI.

此模組在行動平台或WebAssembly 平台上不支援。

exceptiondbm.gnu.error

Raised ondbm.gnu-specific errors, such as I/O errors.KeyError israised for general mapping errors like specifying an incorrect key.

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

Open a GDBM database and return agdbm object.

參數:

  • filename (path-like object) -- 要打開的資料庫檔案

  • 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 appendedto 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': 不要鎖住資料庫。

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

  • mode (int) -- The Unix file access mode of the file (default: octal0o666),used only when the database has to be created.

引發:

error -- 如果一個無效的flag 引數被傳入。

在 3.11 版的變更:filename accepts apath-like object.

dbm.gnu.open_flags

A string of characters theflag parameter ofopen() supports.

gdbm objects behave similar tomappings,butitems() andvalues() methods are not supported.The following methods are also provided:

gdbm.firstkey()

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

gdbm.nextkey(key)

Returns the key that followskey in the traversal. The following code printsevery key in the databasedb, without having to create a list in memory thatcontains them all:

k=db.firstkey()whilekisnotNone:print(k)k=db.nextkey(k)
gdbm.reorganize()

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

gdbm.sync()

When the database has been opened in fast mode, this method forces anyunwritten data to be written to the disk.

gdbm.close()

關閉 GDBM 資料庫。

gdbm.clear()

移除 GDBM 資料庫中所有項目。

在 3.13 版被加入.

dbm.ndbm --- 新資料庫管理器

原始碼：Lib/dbm/ndbm.py

Thedbm.ndbm module provides an interface to theNDBM library.This module can be used with the "classic" NDBM interface or theGDBM compatibility interface.

備註

The file formats created bydbm.gnu anddbm.ndbm are incompatibleand can not be used interchangeably.

警告

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

適用: not Android, not iOS, not WASI.

此模組在行動平台或WebAssembly 平台上不支援。

exceptiondbm.ndbm.error

Raised ondbm.ndbm-specific errors, such as I/O errors.KeyError is raisedfor 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 anndbm object.

參數:

  • 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: octal0o666),used only when the database has to be created.

ndbm objects behave similar tomappings,butitems() andvalues() methods are not supported.The following methods are also provided:

在 3.11 版的變更:Acceptspath-like object for filename.

ndbm.close()

關閉 NDBM 資料庫。

ndbm.clear()

移除 NDBM 資料庫中所有項目。

在 3.13 版被加入.

dbm.dumb --- 可攜式 DBM 實作

原始碼：Lib/dbm/dumb.py

備註

Thedbm.dumb module is intended as a last resort fallback for thedbm module when a more robust module is not available. Thedbm.dumbmodule is not written for speed and is not nearly as heavily used as the otherdatabase modules.

Thedbm.dumb module provides a persistentdict-likeinterface which is written entirely in Python.Unlike otherdbm backends, such asdbm.gnu, noexternal library is required.

dbm.dumb 模組定義了以下項目：

exceptiondbm.dumb.error

Raised ondbm.dumb-specific errors, such as I/O errors.KeyError israised for general mapping errors like specifying an incorrect key.

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

Open adbm.dumb database.The returned database object behaves similar to amapping,in addition to providingsync() andclose()methods.

參數:

  • 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: octal0o666),used only when the database has to be created.

警告

It is possible to crash the Python interpreter when loading a databasewith a sufficiently large/complex entry due to stack depth limitations inPython's AST compiler.

在 3.5 版的變更:open() always creates a new database whenflag is'n'.

在 3.8 版的變更:A database opened read-only ifflag is'r'.A database is not created if it does not exist ifflag is'r' or'w'.

在 3.11 版的變更:filename accepts apath-like object.

In addition to the methods provided by thecollections.abc.MutableMapping class,the following methods are provided:

dumbdbm.sync()

Synchronize the on-disk directory and data files. This method is calledby theshelve.Shelf.sync() method.

dumbdbm.close()

關閉資料庫。