##
7.11.1 Hash, BTree and Record Objects

Once instantiated, hash, btree and record objects support the following 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 the key and return it.

`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.

`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 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 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()`).

`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')
      >>> db.sync()
      0