mirror of
https://github.com/python/cpython.git
synced 2025-10-31 18:28:49 +00:00
122 lines
4.5 KiB
ReStructuredText
122 lines
4.5 KiB
ReStructuredText
|
|
:mod:`gdbm` --- GNU's reinterpretation of dbm
|
|
=============================================
|
|
|
|
.. module:: gdbm
|
|
:platform: Unix
|
|
:synopsis: GNU's reinterpretation of dbm.
|
|
|
|
|
|
.. 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.
|
|
|