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
dbm are incompatible.
The gdbm module provides an interface to the GNU DBM
gdbm objects behave like mappings
(dictionaries), except that keys and values are always strings.
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:
gdbm-specific errors, such as I/O errors. KeyError is raised for general mapping errors like specifying an incorrect key.
gdbmdatabase and return a
gdbmobject. 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 syncronized.
'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
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
In addition to the dictionary-like methods,
gdbm objects have the
gdbm's internal hash values, and won't be sorted by the key values. This method returns the starting key.
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)
gdbmfile, this routine will reorganize the database.
gdbmwill 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.