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:mod:`dbhash` --- DBM-style interface to the BSD database library
=================================================================
.. module:: dbhash
:synopsis: DBM-style interface to the BSD database library.
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
.. index:: module: bsddb
The :mod:`dbhash` module provides a function to open databases using the BSD
``db`` library. This module mirrors the interface of the other Python database
modules that provide access to DBM-style databases. The :mod:`bsddb` module is
required to use :mod:`dbhash`.
This module provides an exception and a function:
.. exception:: error
Exception raised on database errors other than :exc:`KeyError`. It is a synonym
for :exc:`bsddb.error`.
.. function:: open(path[, flag[, mode]])
Open a ``db`` database and return the database object. The *path* argument is
the name of the database file.
The *flag* argument can be:
+---------+-------------------------------------------+
| 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 |
+---------+-------------------------------------------+
For platforms on which the BSD ``db`` library supports locking, an ``'l'``
can be appended to indicate that locking should be used.
The optional *mode* parameter is used to indicate the Unix permission bits that
should be set if a new database must be created; this will be masked by the
current umask value for the process.
.. seealso::
Module :mod:`anydbm`
Generic interface to ``dbm``\ -style databases.
Module :mod:`bsddb`
Lower-level interface to the BSD ``db`` library.
Module :mod:`whichdb`
Utility module used to determine the type of an existing database.
.. _dbhash-objects:
Database Objects
----------------
The database objects returned by :func:`open` provide the methods common to all
the DBM-style databases and mapping objects. The following methods are
available in addition to the standard methods.
.. method:: dbhash.first()
It's possible to loop over every key/value pair in the database using this
method and the :meth:`next` method. The traversal is ordered by the databases
internal hash values, and won't be sorted by the key values. This method
returns the starting key.
.. method:: dbhash.last()
Return the last key/value pair in a database traversal. This may be used to
begin a reverse-order traversal; see :meth:`previous`.
.. method:: dbhash.next()
Returns the key next key/value pair in a database traversal. The following code
prints every key in the database ``db``, without having to create a list in
memory that contains them all::
print(db.first())
for i in range(1, len(db)):
print(db.next())
.. method:: dbhash.previous()
Returns the previous key/value pair in a forward-traversal of the database. In
conjunction with :meth:`last`, this may be used to implement a reverse-order
traversal.
.. method:: dbhash.sync()
This method forces any unwritten data to be written to the disk.
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