# 7.11 `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 is only available on Unix systems, so it is not built by default in the standard Python distribution. Also, there are two incompatible versions of the underlying library. Version 1.85 is widely available, but has some known bugs. Version 2 is not quite as widely used, but does offer some improvements. The `bsddb` module uses the 1.85 interface. Users wishing to use version 2 of the Berkeley DB library will have to modify the source for the module to include db_185.h instead of db.h (db_185.h contains the version 1.85 compatibility interface).

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. 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) 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. 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) 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. 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) 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`.

- 7.11.1 Hash, BTree and Record Objects