# 8.6 `dbm` -- Simple ``database'' interface

Availability: Unix.

The `dbm` module provides an interface to the Unix (`n`)`dbm` library. Dbm objects behave like mappings (dictionaries), except that keys and values are always strings. Printing a dbm object doesn't print the keys and values, and the `items()` and `values()` methods are not supported.

This module can be used with the ``classic'' ndbm interface, the BSD DB compatibility interface, or the GNU GDBM compatibility interface. On Unix, the configure script will attempt to locate the appropriate header file to simplify building this module.

The module defines the following:

exception `error`
  Raised on dbm-specific errors, such as I/O errors. `KeyError` is raised for general mapping errors like specifying an incorrect key.

`library`
  Name of the `ndbm` implementation library used.

`open`(filename[, flag[, mode]])
  Open a dbm database and return a dbm object. The filename argument is the name of the database file (without the .dir or .pag extensions; note that the BSD DB implementation of the interface will append the extension .db and only create one file).

  The optional flag argument must be one of these values:

  Value | Meaning
  --- | ---
  `'r'` | Open existing database for reading only (default)
  `'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 optional mode argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal `0666`.

See Also:

Module `anydbm`:
  Generic interface to `dbm`-style databases.

Module `gdbm`:
  Similar interface to the GNU GDBM library.

Module `whichdb`:
  Utility module used to determine the type of an existing database.