gdbm
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:
gdbm
-specific errors, such as I/O errors. KeyError
is
raised for general mapping errors like specifying an incorrect key.
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).
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
0666
.
In addition to the dictionary-like methods, gdbm
objects have the
following methods:
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.
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)
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.