11.11. bsddb — Interface to Berkeley DB library

2.6 版后已移除: The bsddb module has been removed in Python 3.

The bsddb module provides an interface to the Berkeley DB library. Users can create hash, btree or record based library files using the appropriate open call. Bsddb objects behave generally like dictionaries. Keys and values must be strings, however, so to use other objects as keys or to store other kinds of objects the user must serialize them somehow, typically using marshal.dumps() or pickle.dumps().

The bsddb module requires a Berkeley DB library version from 4.0 thru 4.7.

参见

http://www.jcea.es/programacion/pybsddb.htm

The website with documentation for the bsddb.db Python Berkeley DB interface that closely mirrors the object oriented interface provided in Berkeley DB 4.x itself.

http://www.oracle.com/database/berkeley-db/

The Berkeley DB library.

A more modern DB, DBEnv and DBSequence object interface is available in the bsddb.db module which closely matches the Berkeley DB C API documented at the above URLs. Additional features provided by the bsddb.db API include fine tuning, transactions, logging, and multiprocess concurrent database access.

The following is a description of the legacy bsddb interface compatible with the old Python bsddb module. Starting in Python 2.5 this interface should be safe for multithreaded access. The bsddb.db API is recommended for threading users as it provides better control.

The bsddb module defines the following functions that create objects that access the appropriate type of Berkeley DB file. The first two arguments of each function are the same. For ease of portability, only the first two arguments should be used in most instances.

bsddb.hashopen(filename[, flag[, mode[, pgsize[, ffactor[, nelem[, cachesize[, lorder[, hflags]]]]]]]])

Open the hash format file named filename. Files never intended to be preserved on disk may be created by passing None as the filename. The optional flag identifies the mode used to open the file. It may be 'r' (read only), 'w' (read-write), 'c' (read-write - create if necessary; the default) or 'n' (read-write - truncate to zero length). The other arguments are rarely used and are just passed to the low-level dbopen() function. Consult the Berkeley DB documentation for their use and interpretation.

bsddb.btopen(filename[, flag[, mode[, btflags[, cachesize[, maxkeypage[, minkeypage[, pgsize[, lorder]]]]]]]])

Open the btree format file named filename. Files never intended to be preserved on disk may be created by passing None as the filename. The optional flag identifies the mode used to open the file. It may be 'r' (read only), 'w' (read-write), 'c' (read-write - create if necessary; the default) or 'n' (read-write - truncate to zero length). The other arguments are rarely used and are just passed to the low-level dbopen function. Consult the Berkeley DB documentation for their use and interpretation.

bsddb.rnopen(filename[, flag[, mode[, rnflags[, cachesize[, pgsize[, lorder[, rlen[, delim[, source[, pad]]]]]]]]]])

Open a DB record format file named filename. Files never intended to be preserved on disk may be created by passing None as the filename. The optional flag identifies the mode used to open the file. It may be 'r' (read only), 'w' (read-write), 'c' (read-write - create if necessary; the default) or 'n' (read-write - truncate to zero length). The other arguments are rarely used and are just passed to the low-level dbopen function. Consult the Berkeley DB documentation for their use and interpretation.

注解

Beginning in 2.3 some Unix versions of Python may have a bsddb185 module. This is present only to allow backwards compatibility with systems which ship with the old Berkeley DB 1.85 database library. The bsddb185 module should never be used directly in new code. The module has been removed in Python 3. If you find you still need it look in PyPI.

参见

Module dbhash

DBM-style interface to the bsddb

11.11.1. Hash, BTree and Record Objects

Once instantiated, hash, btree and record objects support the same methods as dictionaries. In addition, they support the methods listed below.

在 2.3.1 版更改: Added dictionary methods.

bsddbobject.close()

Close the underlying file. The object can no longer be accessed. Since there is no open open() method for these objects, to open the file again a new bsddb module open function must be called.

bsddbobject.keys()

Return the list of keys contained in the DB file. The order of the list is unspecified and should not be relied on. In particular, the order of the list returned is different for different file formats.

bsddbobject.has_key(key)

Return 1 if the DB file contains the argument as a key.

bsddbobject.set_location(key)

Set the cursor to the item indicated by key and return a tuple containing the key and its value. For binary tree databases (opened using btopen()), if key does not actually exist in the database, the cursor will point to the next item in sorted order and return that key and value. For other databases, KeyError will be raised if key is not found in the database.

bsddbobject.first()

Set the cursor to the first item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases. This method raises bsddb.error if the database is empty.

bsddbobject.next()

Set the cursor to the next item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases.

bsddbobject.previous()

Set the cursor to the previous item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases. This is not supported on hashtable databases (those opened with hashopen()).

bsddbobject.last()

Set the cursor to the last item in the DB file and return it. The order of keys in the file is unspecified. This is not supported on hashtable databases (those opened with hashopen()). This method raises bsddb.error if the database is empty.

bsddbobject.sync()

Synchronize the database on disk.

Example:

>>> import bsddb
>>> db = bsddb.btopen('spam.db', 'c')
>>> for i in range(10): db['%d'%i] = '%d'% (i*i)
...
>>> db['3']
'9'
>>> db.keys()
['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
>>> db.first()
('0', '0')
>>> db.next()
('1', '1')
>>> db.last()
('9', '81')
>>> db.set_location('2')
('2', '4')
>>> db.previous()
('1', '1')
>>> for k, v in db.iteritems():
...     print k, v
0 0
1 1
2 4
3 9
4 16
5 25
6 36
7 49
8 64
9 81
>>> '8' in db
True
>>> db.sync()
0