mirror of https://github.com/python/cpython
bsddb docs from Skip Montanaro; added interesting links.
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\module{anydbm} is a generic interface to variants of the DBM
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database --- \refmodule{dbhash}\refstmodindex{dbhash} (requires
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\module{bsddb}\refbimodindex{bsddb}),
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\refmodule{bsddb}\refbimodindex{bsddb}),
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\refmodule{gdbm}\refbimodindex{gdbm}, or
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\refmodule{dbm}\refbimodindex{dbm}. If none of these modules is
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installed, the slow-but-simple implementation in module
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\section{\module{bsddb} ---
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Interface to Berkeley DB library}
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\declaremodule{extension}{bsddb}
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\platform{Unix, Windows}
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\modulesynopsis{Interface to Berkeley DB database library}
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\sectionauthor{Skip Montanaro}{skip@mojam.com}
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The \module{bsddb} module provides an interface to the Berkeley DB library.
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Users can create hash, btree or record based library files using the
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appropriate open call. Bsddb objects behave generally like dictionaries.
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Keys and values must be strings, however, so to use other objects as keys or
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to store other kinds of objects the user must serialize them somehow,
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typically using marshal.dumps or pickle.dumps.
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The \module{bsddb} module is only available on \UNIX{} systems, so it is not
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built by default in the standard Python distribution. Also, there are two
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incompatible versions of the underlying library. Version 1.85 is widely
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available, but has some known bugs. Version 2 is not quite as widely used,
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but does offer some improvements. The \module{bsddb} module uses the 1.85
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interface. Users wishing to use version 2 of the Berkeley DB library will
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have to modify the source for the module to include db_185.h instead of
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db.h.
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The \module{bsddb} module defines the following functions that create
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objects that access the appropriate type of Berkeley DB file. The first two
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arguments of each function are the same. For ease of portability, only the
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first two arguments should be used in most instances.
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\begin{funcdesc}{hashopen}{filename\optional{, flag\optional{,
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mode\optional{, bsize\optional{, ffactor\optional{, nelem\optional{,
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cachesize\optional{, hash\optional{, lorder}}}}}}}}}
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Open the hash format file named \var{filename}. The optional \var{flag}
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identifies the mode used to open the file. It may be ``r'' (read only),
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``w'' (read-write), ``c'' (read-write - create if necessary) or ``n''
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(read-write - truncate to zero length). The other arguments are rarely used
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and are just passed to the low-level dbopen function. Consult the
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Berkeley DB documentation for their use and interpretation.
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\end{funcdesc}
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\begin{funcdesc}{btopen}{filename\optional{, flag\optional{,
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mode\optional{, btflags\optional{, cachesize\optional{, maxkeypage\optional{,
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minkeypage\optional{, psize\optional{, lorder}}}}}}}}}
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Open the btree format file named \var{filename}. The optional \var{flag}
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identifies the mode used to open the file. It may be ``r'' (read only),
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``w'' (read-write), ``c'' (read-write - create if necessary) or ``n''
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(read-write - truncate to zero length). The other arguments are rarely used
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and are just passed to the low-level dbopen function. Consult the
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Berkeley DB documentation for their use and interpretation.
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\end{funcdesc}
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\begin{funcdesc}{rnopen}{filename\optional{, flag\optional{, mode\optional{,
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rnflags\optional{, cachesize\optional{, psize\optional{, lorder\optional{,
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reclen\optional{, bval\optional{, bfname}}}}}}}}}}
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Open a DB record format file named \var{filename}. The optional \var{flag}
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identifies the mode used to open the file. It may be ``r'' (read only),
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``w'' (read-write), ``c'' (read-write - create if necessary) or ``n''
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(read-write - truncate to zero length). The other arguments are rarely used
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and are just passed to the low-level dbopen function. Consult the
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Berkeley DB documentation for their use and interpretation.
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\end{funcdesc}
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\begin{seealso}
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\seemodule{dbhash}{DBM-style interface to the \module{bsddb}}
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\end{seealso}
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\subsection{Hash, BTree and Record Objects \label{bsddb-objects}}
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Once instantiated, hash, btree and record objects support the following
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methods:
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\begin{methoddesc}{close}{}
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Close the underlying file. The object can no longer be accessed. Since
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there is no open \method{open} method for these objects, to open the file
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again a new \module{bsddb} module open function must be called.
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\end{methoddesc}
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\begin{methoddesc}{keys}{}
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Return the list of keys contained in the DB file. The order of the list is
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unspecified and should not be relied on. In particular, the order of the
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list returned is different for different file formats.
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\end{methoddesc}
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\begin{methoddesc}{has_key}{key}
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Return 1 if the DB file contains the argument as a key.
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\end{methoddesc}
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\begin{methoddesc}{set_location}{key}
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Set the cursor to the item indicated by the key and return it.
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\end{methoddesc}
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\begin{methoddesc}{first}{}
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Set the cursor to the first item in the DB file and return it. The order of
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keys in the file is unspecified.
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\end{methoddesc}
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\begin{methoddesc}{next}{}
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Set the cursor to the next item in the DB file and return it. The order of
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keys in the file is unspecified.
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\end{methoddesc}
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\begin{methoddesc}{previous}{}
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Set the cursor to the first item in the DB file and return it. The order of
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keys in the file is unspecified.
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\end{methoddesc}
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\begin{methoddesc}{last}{}
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Set the cursor to the last item in the DB file and return it. The order of
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keys in the file is unspecified.
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\end{methoddesc}
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\begin{methoddesc}{sync}{}
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Synchronize the database on disk.
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\end{methoddesc}
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Example:
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\begin{verbatim}
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>>> import bsddb
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>>> db = bsddb.btopen('/tmp/spam.db', 'c')
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>>> for i in range(10): db['%d'%i] = '%d'% (i*i)
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...
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>>> db['3']
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'9'
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>>> db.keys()
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['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
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>>> db.first()
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('0', '0')
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>>> db.next()
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('1', '1')
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>>> db.last()
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('9', '81')
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>>> db.set_location('2')
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('2', '4')
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>>> db.previous()
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('1', '1')
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>>> db.sync()
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0
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\end{verbatim}
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@ -10,7 +10,7 @@
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The \module{dbhash} module provides a function to open databases using
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the BSD \code{db} library. This module mirrors the interface of the
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other Python database modules that provide access to DBM-style
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databases. The \module{bsddb}\refbimodindex{bsddb} module is required
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databases. The \refmodule{bsddb}\refbimodindex{bsddb} module is required
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to use \module{dbhash}.
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This module provides an exception and a function:
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\begin{seealso}
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\seemodule{anydbm}{Generic interface to \code{dbm}-style databases.}
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\seemodule{bsddb}{Lower-level interface to the BSD \code{db} library.}
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\seemodule{whichdb}{Utility module used to determine the type of an
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existing database.}
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\end{seealso}
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