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7.9.1 Database Objects

The database objects returned by `open()` provide the methods common to all the DBM-style databases. The following methods are available in addition to the standard methods.

`first` ()
  It's possible to loop over every key in the database using this method and the `next()` method. The traversal is ordered by the databases internal hash values, and won't be sorted by the key values. This method returns the starting key.

`last` ()
  Return the last key in a database traversal. This may be used to begin a reverse-order traversal; see `previous()`.

`next` (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.first()
        while k != None:
            print k
            k = db.next(k)

`previous` (key)
  Return the key that comes before key in a forward-traversal of the database. In conjunction with `last()`, this may be used to implement a reverse-order traversal.

`sync` ()
  This method forces any unwritten data to be written to the disk.