|
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 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 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.
|
