# 13.11 `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()`.

The `bsddb` module requires a Berkeley DB library version from 3.3 thru 4.4.

See Also:

http://pybsddb.sourceforge.net/
  The website with documentation for the `bsddb.db` 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 Berkeley DB library.

A more modern DB, DBEnv and DBSequence object interface is available in the `bsddb.db` module which closely matches the Sleepycat 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.

`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), "`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.

`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.

`rnopen`( | filename[, flag[, mode[, rnflags[, cachesize[, pgsize[, 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), "`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.

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.

See Also:

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