added __doc__ strings etc.

Lib/shelve.py

@@ -1,9 +1,43 @@
-"""Manage shelves of pickled objects."""
+"""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
+
+	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.
+"""
 
 import pickle
 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
@@ -18,7 +52,8 @@ class Shelf:
 		return self.dict.has_key(key)
 	
 	def __getitem__(self, key):
-		return pickle.Unpickler(StringIO.StringIO(self.dict[key])).load()
+		f = StringIO.StringIO(self.dict[key])
+		return pickle.Unpickler(f).load()
 	
 	def __setitem__(self, key, value):
 		f = StringIO.StringIO()
@@ -30,14 +65,31 @@ class Shelf:
 		del self.dict[key]
 	
 	def close(self):
-		self.db.close()
+		if hasattr(self.db, 'close'):
+			self.db.close()
 		self.db = None
 
-class DbShelf(Shelf):
-	
-	def __init__(self, file):
-		import anydbm
-		Shelf.__init__(self, anydbm.open(file))
+	def __del__(self):
+		self.close()
 
-def open(file):
-	return DbShelf(file)
+
+class DbShelf(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):
+		import anydbm
+		Shelf.__init__(self, anydbm.open(filename))
+
+
+def open(filename):
+	"""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 DbShelf(filename)