\section{\module{gdbm} ---         GNU's reinterpretation of dbm} \declaremodule{builtin}{gdbm}  \platform{Unix}\modulesynopsis{GNU's reinterpretation of dbm.}  This module is quite similar to the \refmodule{dbm}\refbimodindex{dbm}module, but uses \code{gdbm} instead to provide some additionalfunctionality.  Please note that the file formats created by\code{gdbm} and \code{dbm} are incompatible. The \module{gdbm} module provides an interface to the GNU DBMlibrary.  \code{gdbm} objects behave like mappings(dictionaries), except that keys and values are always strings.Printing a \code{gdbm} object doesn't print the keys and values, andthe \method{items()} and \method{values()} methods are not supported. The module defines the following constant and functions: \begin{excdesc}{error}Raised on \code{gdbm}-specific errors, such as I/O errors.\exception{KeyError} is raised for general mapping errors likespecifying an incorrect key.\end{excdesc} \begin{funcdesc}{open}{filename, \optional{flag, \optional{mode}}}Open a \code{gdbm} database and return a \code{gdbm} object.  The\var{filename} argument is the name of the database file. The optional \var{flag} argument can be\code{'r'} (to open an existing database for reading only --- default),\code{'w'} (to open an existing database for reading and writing),\code{'c'} (which creates the database if it doesn't exist), or\code{'n'} (which always creates a new empty database). The following additional characters may be appended to the flag tocontrol how the database is opened: \begin{itemize}\item \code{'f'} --- Open the database in fast mode.  Writes to the database                     will not be synchronized.\item \code{'s'} --- Synchronized mode. This will cause changes to the database                     will be immediately written to the file.\item \code{'u'} --- Do not lock database. \end{itemize} Not all flags are valid for all versions of \code{gdbm}.  Themodule constant \code{open_flags} is a string of supported flagcharacters.  The exception \exception{error} is raised if an invalidflag is specified. The optional \var{mode} argument is the \UNIX{} mode of the file, usedonly when the database has to be created.  It defaults to octal\code{0666}.\end{funcdesc} In addition to the dictionary-like methods, \code{gdbm} objects have thefollowing methods: \begin{funcdesc}{firstkey}{}It's possible to loop over every key in the database using this method and the \method{nextkey()} method.  The traversal is ordered by\code{gdbm}'s internal hash values, and won't be sorted by the keyvalues.  This method returns the starting key.\end{funcdesc} \begin{funcdesc}{nextkey}{key}Returns the key that follows \var{key} in the traversal.  Thefollowing code prints every key in the database \code{db}, withouthaving to create a list in memory that contains them all: \begin{verbatim}k = db.firstkey()while k != None:    print k    k = db.nextkey(k)\end{verbatim}\end{funcdesc} \begin{funcdesc}{reorganize}{}If you have carried out a lot of deletions and would like to shrinkthe space used by the \code{gdbm} file, this routine will reorganizethe database.  \code{gdbm} will not shorten the length of a databasefile except by using this reorganization; otherwise, deleted filespace will be kept and reused as new (key, value) pairs are added.\end{funcdesc} \begin{funcdesc}{sync}{}When the database has been opened in fast mode, this method forces any unwritten data to be written to the disk.\end{funcdesc}  \begin{seealso}  \seemodule{anydbm}{Generic interface to \code{dbm}-style databases.}  \seemodule{whichdb}{Utility module used to determine the type of an                      existing database.}\end{seealso}