# 7.13 `bsddb` -- Interface to Berkeley DB library

Availability: Unix, Windows.

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.

Starting with Python 2.3 the `bsddb` module requires the Berkeley DB library version 3.1 or later (it is known to work with 3.1 thru 4.1 at the time of this writing).

See Also:

http://pybsddb.sourceforge.net/
  Website with documentation for the new python Berkeley DB interface that closely mirrors the sleepycat object oriented interface provided in Berkeley DB 3 and 4.

http://www.sleepycat.com/
  Sleepycat Software produces the modern Berkeley DB library.

The following is a description of the legacy `bsddb` interface compatible with the old python bsddb module. For details about the more modern Db and DbEnv object oriented interface see the above mentioned pybsddb URL.

Warning: This legacy interface is not thread safe in python 2.3.x or earlier. Data corruption, core dumps or deadlocks may occur if you attempt multi-threaded access. You must use the modern pybsddb interface linked to above if you need multi-threaded or multi-process database access.

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.

`hashopen`( | filename[, flag[, mode[, bsize[, ffactor[, nelem[, cachesize[, hash[, lorder]]]]]]]])

  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, default), "`w`" (read-write) , "`c`" (read-write - create if necessary) 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.

`btopen`( | filename[, flag[, mode[, btflags[, cachesize[, maxkeypage[, minkeypage[, psize[, 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, default), "`w`" (read-write), "`c`" (read-write - create if necessary) 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.

`rnopen`( | filename[, flag[, mode[, rnflags[, cachesize[, psize[, lorder[, reclen[, bval[, bfname]]]]]]]]])

  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, default), "`w`" (read-write), "`c`" (read-write - create if necessary) 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.

See Also:

Module `dbhash`:
  DBM-style interface to the `bsddb`.

Note: 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.