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, the slow-but-simple implementation in module dbm.dumb will be used. There is a third party interface to the Oracle Berkeley DB.

exception dbm.error

A tuple containing the exceptions that can be raised by each of the supported modules, with a unique exception also named dbm.error as the first item --- the latter is used when dbm.error is raised.

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.

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 a path-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, 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.

在 3.11 版的變更: file 接受一個類路徑物件。

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.

These objects also support being used in a with statement, which will automatically close them when done.

在 3.2 版的變更: get() and setdefault() methods are now available for all dbm backends.

在 3.4 版的變更: Added native support for the context management protocol to the objects returned by open().

在 3.8 版的變更: Deleting a key from a read-only database raises a database module specific exception instead of KeyError.

在 3.13 版的變更: clear() 方法現在可用於所有 dbm 後端。

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

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.

也參考

shelve 模組

Persistence module which stores non-string data.

The individual submodules are described in the following sections.

dbm.sqlite3 --- dbm 的 SQLite 後端

在 3.13 版被加入.

原始碼：Lib/dbm/sqlite3.py

This module uses the standard library