13.11.1 Hash, BTree and Record Objects

Python 2.5

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13.11.1 Hash, BTree and Record Objects

Once instantiated, hash, btree and record objects support the same methods as dictionaries. In addition, they support the methods listed below. Changed in version 2.3.1: Added dictionary methods.

close( ): Close the underlying file. The object can no longer be accessed. Since there is no open open method for these objects, to open the file again a new bsddb module open function must be called.

keys( ): Return the list of keys contained in the DB file. The order of the list is unspecified and should not be relied on. In particular, the order of the list returned is different for different file formats.

has_key( key): Return 1 if the DB file contains the argument as a key.

set_location( key): Set the cursor to the item indicated by key and return a tuple containing the key and its value. For binary tree databases (opened using btopen()), if key does not actually exist in the database, the cursor will point to the next item in sorted order and return that key and value. For other databases, KeyError will be raised if key is not found in the database.

first( ): Set the cursor to the first item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases. This method raises bsddb.error if the database is empty.

next( ): Set the cursor to the next item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases.

previous( ): Set the cursor to the previous item in the DB file and return it. The order of keys in the file is unspecified, except in the case of B-Tree databases. This is not supported on hashtable databases (those opened with hashopen()).

last( ): Set the cursor to the last item in the DB file and return it. The order of keys in the file is unspecified. This is not supported on hashtable databases (those opened with hashopen()). This method raises bsddb.error if the database is empty.

sync( ): Synchronize the database on disk.

Example:

>>> import bsddb
>>> db = bsddb.btopen('/tmp/spam.db', 'c')
>>> for i in range(10): db['%d'%i] = '%d'% (i*i)
... 
>>> db['3']
'9'
>>> db.keys()
['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
>>> db.first()
('0', '0')
>>> db.next()
('1', '1')
>>> db.last()
('9', '81')
>>> db.set_location('2')
('2', '4')
>>> db.previous() 
('1', '1')
>>> for k, v in db.iteritems():
...     print k, v
0 0
1 1
2 4
3 9
4 16
5 25
6 36
7 49
8 64
9 81
>>> '8' in db
True
>>> db.sync()
0

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