/Doc/library/gdbm.rst
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- :mod:`gdbm` --- GNU's reinterpretation of dbm
- =============================================
- .. module:: gdbm
- :platform: Unix
- :synopsis: GNU's reinterpretation of dbm.
- .. note::
- The :mod:`gdbm` module has been renamed to :mod:`dbm.gnu` in Python 3.0. The
- :term:`2to3` tool will automatically adapt imports when converting your
- sources to 3.0.
- .. index:: module: dbm
- This module is quite similar to the :mod:`dbm` module, but uses ``gdbm`` instead
- to provide some additional functionality. Please note that the file formats
- created by ``gdbm`` and ``dbm`` are incompatible.
- The :mod:`gdbm` module provides an interface to the GNU DBM library. ``gdbm``
- objects behave like mappings (dictionaries), except that keys and values are
- always strings. Printing a ``gdbm`` object doesn't print the keys and values,
- and the :meth:`items` and :meth:`values` methods are not supported.
- The module defines the following constant and functions:
- .. exception:: error
- Raised on ``gdbm``\ -specific errors, such as I/O errors. :exc:`KeyError` is
- raised for general mapping errors like specifying an incorrect key.
- .. function:: open(filename, [flag, [mode]])
- Open a ``gdbm`` database and return a ``gdbm`` object. The *filename* argument
- is the name of the database file.
- The optional *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 |
- +---------+-------------------------------------------+
- The following additional characters may be appended to the flag to control
- how the database is opened:
- +---------+--------------------------------------------+
- | Value | Meaning |
- +=========+============================================+
- | ``'f'`` | Open the database in fast mode. Writes |
- | | to the database will not be synchronized. |
- +---------+--------------------------------------------+
- | ``'s'`` | Synchronized mode. This will cause changes |
- | | to the database to be immediately written |
- | | to the file. |
- +---------+--------------------------------------------+
- | ``'u'`` | Do not lock database. |
- +---------+--------------------------------------------+
- Not all flags are valid for all versions of ``gdbm``. The module constant
- :const:`open_flags` is a string of supported flag characters. The exception
- :exc:`error` is raised if an invalid flag is specified.
- 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``.
- In addition to the dictionary-like methods, ``gdbm`` objects have the following
- methods:
- .. function:: firstkey()
- It's possible to loop over every key in the database using this method and the
- :meth:`nextkey` method. The traversal is ordered by ``gdbm``'s internal hash
- values, and won't be sorted by the key values. This method returns the starting
- key.
- .. function:: nextkey(key)
- Returns the key that follows *key* in the traversal. The following code prints
- every key in the database ``db``, without having to create a list in memory that
- contains them all::
- k = db.firstkey()
- while k != None:
- print k
- k = db.nextkey(k)
- .. function:: reorganize()
- If you have carried out a lot of deletions and would like to shrink the space
- used by the ``gdbm`` file, this routine will reorganize the database. ``gdbm``
- will not shorten the length of a database file except by using this
- reorganization; otherwise, deleted file space will be kept and reused as new
- (key, value) pairs are added.
- .. function:: sync()
- When the database has been opened in fast mode, this method forces any
- unwritten data to be written to the disk.
- .. seealso::
- Module :mod:`anydbm`
- Generic interface to ``dbm``\ -style databases.
- Module :mod:`whichdb`
- Utility module used to determine the type of an existing database.