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 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.

可用性: 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)

打開一個 SQLite 資料庫。

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: 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.

也提供了以下方法：

sqlite3.close()

關閉 SQLite 資料庫。

dbm.gnu --- GNU 資料庫管理器

原始碼：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.

備註

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

可用性: not Android, not iOS, not WASI.

此模組在行動平台或 WebAssembly 平台上不支援。

可用性: 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, /)

打開一個 GDBM 資料庫，並回傳一個 gdbm 物件。

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 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': 不要鎖住資料庫。

    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.

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 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.

在 3.2 版的變更: 新增了 get() 和 setdefault() 方法。

在 3.13 版的變更: 新增了 clear() 方法。

也提供了以下方法：

gdbm.close()

關閉 GDBM 資料庫。

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)

Returns the key that follows key in the traversal. The following code prints every key in the database db, without having to create a list in memory that contains them all:

k = db.