This module is quite similar to the
dbm module, but uses
to provide some additional functionality. Please note that the file formats
dbm are incompatible.
gdbm module provides an interface to the GNU DBM library.
objects behave like mappings (dictionaries), except that keys and values are
always strings. Printing a
gdbm object doesn’t print the keys and values,
values() methods are not supported.
The module defines the following constant and functions:
gdbm-specific errors, such as I/O errors.
KeyErroris raised for general mapping errors like specifying an incorrect key.
open(filename[, flag[, mode]])¶
gdbmdatabase and return a
gdbmobject. The filename argument is the name of the database file.
The optional flag argument can be:
Open existing database for reading only (default)
Open existing database for reading and writing
Open database for reading and writing, creating it if it doesn’t exist
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:
Open the database in fast mode. Writes to the database will not be synchronized.
Synchronized mode. This will cause changes to the database to be immediately written to the file.
Do not lock database.
Not all flags are valid for all versions of
gdbm. The module constant
open_flagsis a string of supported flag characters. The exception
erroris 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 following
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
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.
When the database has been opened in fast mode, this method forces any unwritten data to be written to the disk.