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-\section{Standard Module \module{shelve}}
-\label{module-shelve}
-\stmodindex{shelve}
-
-A ``shelf'' is a persistent, dictionary-like object. The difference
-with ``dbm'' databases is that the values (not the keys!) in a shelf
-can be essentially arbitrary Python objects --- anything that the
-\code{pickle} module can handle. This includes most class instances,
-recursive data types, and objects containing lots of shared
-sub-objects. The keys are ordinary strings.
-\refstmodindex{pickle}
-
-To summarize the interface (\code{key} is a string, \code{data} is an
-arbitrary object):
-
-\begin{verbatim}
-import shelve
-
-d = shelve.open(filename) # open, with (g)dbm filename -- no suffix
-
-d[key] = data # store data at key (overwrites old data if
- # using an existing key)
-data = d[key] # retrieve data at key (raise KeyError if no
- # such key)
-del d[key] # delete data stored at key (raises KeyError
- # if no such key)
-flag = d.has_key(key) # true if the key exists
-list = d.keys() # a list of all existing keys (slow!)
-
-d.close() # close it
-\end{verbatim}
-%
-Restrictions:
-
-\begin{itemize}
-
-\item
-The choice of which database package will be used (e.g. \code{dbm} or
-\code{gdbm})
-depends on which interface is available. Therefore it isn't safe to
-open the database directly using \code{dbm}. The database is also
-(unfortunately) subject to the limitations of \code{dbm}, if it is used ---
-this means that (the pickled representation of) the objects stored in
-the database should be fairly small, and in rare cases key collisions
-may cause the database to refuse updates.
-\refbimodindex{dbm}
-\refbimodindex{gdbm}
-
-\item
-Dependent on the implementation, closing a persistent dictionary may
-or may not be necessary to flush changes to disk.
-
-\item
-The \code{shelve} module does not support \emph{concurrent} read/write
-access to shelved objects. (Multiple simultaneous read accesses are
-safe.) When a program has a shelf open for writing, no other program
-should have it open for reading or writing. \UNIX{} file locking can
-be used to solve this, but this differs across \UNIX{} versions and
-requires knowledge about the database implementation used.
-
-\end{itemize}