symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/gdbm.rst
author johnathan.white@2718R8BGH51.accenture.com
Mon, 08 Mar 2010 18:45:03 +0000
changeset 46 b6935a90ca64
parent 1 2fb8b9db1c86
permissions -rw-r--r--
Modify framebuffer and NGA framebuffer to read screen size from board model dtb file. Optimise memory usuage of frame buffer Add example minigui application with hooks to profiler (which writes results to S:\). Modified NGA framebuffer to run its own dfc queue at high priority
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:mod:`gdbm` --- GNU's reinterpretation of dbm
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=============================================
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.. module:: gdbm
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   :platform: Unix
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   :synopsis: GNU's reinterpretation of dbm.
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.. note::
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   The :mod:`gdbm` module has been renamed to :mod:`dbm.gnu` in Python 3.0.  The
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   :term:`2to3` tool will automatically adapt imports when converting your
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   sources to 3.0.
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.. index:: module: dbm
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This module is quite similar to the :mod:`dbm` module, but uses ``gdbm`` instead
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to provide some additional functionality.  Please note that the file formats
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created by ``gdbm`` and ``dbm`` are incompatible.
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The :mod:`gdbm` module provides an interface to the GNU DBM library.  ``gdbm``
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objects behave like mappings (dictionaries), except that keys and values are
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always strings. Printing a ``gdbm`` object doesn't print the keys and values,
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and the :meth:`items` and :meth:`values` methods are not supported.
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The module defines the following constant and functions:
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.. exception:: error
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   Raised on ``gdbm``\ -specific errors, such as I/O errors. :exc:`KeyError` is
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   raised for general mapping errors like specifying an incorrect key.
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.. function:: open(filename, [flag, [mode]])
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   Open a ``gdbm`` database and return a ``gdbm`` object.  The *filename* argument
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   is the name of the database file.
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   The optional *flag* argument can be:
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   +---------+-------------------------------------------+
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   | Value   | Meaning                                   |
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   +=========+===========================================+
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   | ``'r'`` | Open existing database for reading only   |
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   |         | (default)                                 |
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   +---------+-------------------------------------------+
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   | ``'w'`` | Open existing database for reading and    |
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   |         | writing                                   |
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   +---------+-------------------------------------------+
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   | ``'c'`` | Open database for reading and writing,    |
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   |         | creating it if it doesn't exist           |
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   +---------+-------------------------------------------+
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   | ``'n'`` | Always create a new, empty database, open |
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   |         | for reading and writing                   |
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   +---------+-------------------------------------------+
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   The following additional characters may be appended to the flag to control
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   how the database is opened:
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   +---------+--------------------------------------------+
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   | Value   | Meaning                                    |
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   +=========+============================================+
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   | ``'f'`` | Open the database in fast mode.  Writes    |
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   |         | to the database will not be synchronized.  |
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   +---------+--------------------------------------------+
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   | ``'s'`` | Synchronized mode. This will cause changes |
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   |         | to the database to be immediately written  |
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   |         | to the file.                               |
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   +---------+--------------------------------------------+
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   | ``'u'`` | Do not lock database.                      |
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   +---------+--------------------------------------------+
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   Not all flags are valid for all versions of ``gdbm``.  The module constant
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   :const:`open_flags` is a string of supported flag characters.  The exception
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   :exc:`error` is raised if an invalid flag is specified.
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   The optional *mode* argument is the Unix mode of the file, used only when the
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   database has to be created.  It defaults to octal ``0666``.
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In addition to the dictionary-like methods, ``gdbm`` objects have the following
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methods:
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.. function:: firstkey()
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   It's possible to loop over every key in the database using this method  and the
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   :meth:`nextkey` method.  The traversal is ordered by ``gdbm``'s internal hash
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   values, and won't be sorted by the key values.  This method returns the starting
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   key.
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.. function:: nextkey(key)
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   Returns the key that follows *key* in the traversal.  The following code prints
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   every key in the database ``db``, without having to create a list in memory that
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   contains them all::
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      k = db.firstkey()
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      while k != None:
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          print k
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          k = db.nextkey(k)
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.. function:: reorganize()
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   If you have carried out a lot of deletions and would like to shrink the space
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   used by the ``gdbm`` file, this routine will reorganize the database.  ``gdbm``
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   will not shorten the length of a database file except by using this
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   reorganization; otherwise, deleted file space will be kept and reused as new
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   (key, value) pairs are added.
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.. function:: sync()
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   When the database has been opened in fast mode, this method forces any
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   unwritten data to be written to the disk.
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.. seealso::
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   Module :mod:`anydbm`
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      Generic interface to ``dbm``\ -style databases.
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   Module :mod:`whichdb`
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      Utility module used to determine the type of an existing database.
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