author | johnathan.white@2718R8BGH51.accenture.com |
Mon, 08 Mar 2010 18:45:03 +0000 | |
changeset 46 | b6935a90ca64 |
parent 1 | 2fb8b9db1c86 |
permissions | -rw-r--r-- |
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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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102 |
|
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.. function:: reorganize() |
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|
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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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108 |
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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111 |
|
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112 |
|
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.. function:: sync() |
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114 |
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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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117 |
|
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118 |
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.. seealso:: |
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120 |
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Module :mod:`anydbm` |
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Generic interface to ``dbm``\ -style databases. |
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123 |
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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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126 |