Availability: Unix.
This module is quite similar to the 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 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 items() and 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.
KeyError is raised for general mapping errors like
specifying an incorrect key.
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
'r' (to open an existing database for reading only -- default),
'w' (to open an existing database for reading and writing),
'c' (which creates the database if it doesn't exist), or
'n' (which always creates a new empty database).
The following additional characters may be appended to the flag to
control how the database is opened:
'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
will be immediately written to the file.
'u' -- Do not lock database.
Not all flags are valid for all versions of gdbm . The
module constant open_flags is a string of supported flag
characters. The exception 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:
-
It's possible to loop over every key in the database using this method
and the 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.
-
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)
-
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.
-
When the database has been opened in fast mode, this method forces any
unwritten data to be written to the disk.
See Also:
- Module anydbm:
- Generic interface to
dbm -style databases.
- Module whichdb:
- Utility module used to determine the type of an
existing database.
Release 2.5.2, documentation updated on 21st February, 2008.
See About this document... for information on suggesting changes.
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