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).
Appending "f" to the flag opens the database in fast mode; altered data will not automatically be written to the disk after every change. This results in faster writes to the database, but may result in an inconsistent database if the program crashes while the database is still open. Use the sync() method to force any unwritten data to be written to the disk.
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.