\section{\module{dbhash} ---         DBM-style interface to the BSD database library} \declaremodule{standard}{dbhash}\modulesynopsis{DBM-style interface to the BSD database library.}\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}  The \module{dbhash} module provides a function to open databases usingthe BSD \code{db} library.  This module mirrors the interface of theother Python database modules that provide access to DBM-styledatabases.  The \refmodule{bsddb}\refbimodindex{bsddb} module is required to use \module{dbhash}. This module provides an exception and a function:  \begin{excdesc}{error}  Exception raised on database errors other than  \exception{KeyError}.  It is a synonym for \exception{bsddb.error}.\end{excdesc} \begin{funcdesc}{open}{path\optional{, flag\optional{, mode}}}  Open a \code{db} database and return the database object.  The  \var{path} argument is the name of the database file.   The \var{flag} argument can be  \code{'r'} (the default), \code{'w'},  \code{'c'} (which creates the database if it doesn't exist), or  \code{'n'} (which always creates a new empty database).  For platforms on which the BSD \code{db} library supports locking,  an \character{l} can be appended to indicate that locking should be  used.   The optional \var{mode} parameter is used to indicate the \UNIX{}  permission bits that should be set if a new database must be  created; this will be masked by the current umask value for the  process.\end{funcdesc}  \begin{seealso}  \seemodule{anydbm}{Generic interface to \code{dbm}-style databases.}  \seemodule{bsddb}{Lower-level interface to the BSD \code{db} library.}  \seemodule{whichdb}{Utility module used to determine the type of an                      existing database.}\end{seealso}  \subsection{Database Objects \label{dbhash-objects}} The database objects returned by \function{open()} provide the methods common to all the DBM-style databases and mapping objects.  The followingmethods are available in addition to the standard methods. \begin{methoddesc}[dbhash]{first}{}  It's possible to loop over every key/value pair in the database using  this method   and the \method{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.\end{methoddesc} \begin{methoddesc}[dbhash]{last}{}  Return the last key/value pair in a database traversal.  This may be used to  begin a reverse-order traversal; see \method{previous()}.\end{methoddesc} \begin{methoddesc}[dbhash]{next}{}  Returns the key next key/value pair in a database traversal.  The  following code prints every key in the database \code{db}, without  having to create a list in memory that contains them all: \begin{verbatim}print db.first()for i in xrange(1, len(db)):    print db.next()\end{verbatim}\end{methoddesc} \begin{methoddesc}[dbhash]{previous}{}  Returns the previous key/value pair in a forward-traversal of the database.  In conjunction with \method{last()}, this may be used to implement  a reverse-order traversal.\end{methoddesc} \begin{methoddesc}[dbhash]{sync}{}  This method forces any unwritten data to be written to the disk.\end{methoddesc}