home *** CD-ROM | disk | FTP | other *** search
- """Manage shelves of pickled objects.
-
- 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 arbitrary
- object):
-
- 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
-
- Dependent on the implementation, closing a persistent dictionary may
- or may not be necessary to flush changes to disk.
- """
-
- # Try using cPickle and cStringIO if available.
-
- try:
- from cPickle import Pickler, Unpickler
- except ImportError:
- from pickle import Pickler, Unpickler
-
- try:
- from cStringIO import StringIO
- except ImportError:
- from StringIO import StringIO
-
-
- class Shelf:
- """Base class for shelf implementations.
-
- This is initialized with a dictionary-like object.
- See the module's __doc__ string for an overview of the interface.
- """
-
- def __init__(self, dict):
- self.dict = dict
-
- def keys(self):
- return self.dict.keys()
-
- def __len__(self):
- return len(self.dict)
-
- def has_key(self, key):
- return self.dict.has_key(key)
-
- def __getitem__(self, key):
- f = StringIO(self.dict[key])
- return Unpickler(f).load()
-
- def __setitem__(self, key, value):
- f = StringIO()
- p = Pickler(f)
- p.dump(value)
- self.dict[key] = f.getvalue()
-
- def __delitem__(self, key):
- del self.dict[key]
-
- def close(self):
- try:
- self.dict.close()
- except:
- pass
- self.dict = 0
-
- def __del__(self):
- self.close()
-
- def sync(self):
- if hasattr(self.dict, 'sync'):
- self.dict.sync()
-
-
- class BsdDbShelf(Shelf):
- """Shelf implementation using the "BSD" db interface.
-
- This adds methods first(), next(), previous(), last() and
- set_location() that have no counterpart in [g]dbm databases.
-
- The actual database must be opened using one of the "bsddb"
- modules "open" routines (i.e. bsddb.hashopen, bsddb.btopen or
- bsddb.rnopen) and passed to the constructor.
-
- See the module's __doc__ string for an overview of the interface.
- """
-
- def __init__(self, dict):
- Shelf.__init__(self, dict)
-
- def set_location(self, key):
- (key, value) = self.dict.set_location(key)
- f = StringIO(value)
- return (key, Unpickler(f).load())
-
- def next(self):
- (key, value) = self.dict.next()
- f = StringIO(value)
- return (key, Unpickler(f).load())
-
- def previous(self):
- (key, value) = self.dict.previous()
- f = StringIO(value)
- return (key, Unpickler(f).load())
-
- def first(self):
- (key, value) = self.dict.first()
- f = StringIO(value)
- return (key, Unpickler(f).load())
-
- def last(self):
- (key, value) = self.dict.last()
- f = StringIO(value)
- return (key, Unpickler(f).load())
-
-
- class DbfilenameShelf(Shelf):
- """Shelf implementation using the "anydbm" generic dbm interface.
-
- This is initialized with the filename for the dbm database.
- See the module's __doc__ string for an overview of the interface.
- """
-
- def __init__(self, filename, flag='c'):
- import anydbm
- Shelf.__init__(self, anydbm.open(filename, flag))
-
-
- def open(filename, flag='c'):
- """Open a persistent dictionary for reading and writing.
-
- Argument is the filename for the dbm database.
- See the module's __doc__ string for an overview of the interface.
- """
-
- return DbfilenameShelf(filename, flag)
-