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 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. To
summarize the interface ( key is a string, data is an 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 - The choice
of which database package will be used (e.g. dbm or gdbm)
depends on which interface is available. Therefore it is not
safe to open the database directly using dbm. The