"""Version of shelve that uses files in a directory with binary pickle format

Allows simultaneous read-write access to the data since
the OS allows multiple processes to have access to the
file system.

$Id: dirshelve.py,v 1.2 2000/11/27 22:31:03 rlw Exp $

XXX keys, len may be incorrect if directory database is modified
XXX by another process after open

R. White, 2000 Sept 26
"""

import dirdbm, shelve

# tuple of errors that can be raised
error = (dirdbm.error, )

class Shelf(shelve.Shelf):
	"""Extension of Shelf using binary pickling"""

	def __getitem__(self, key):
		f = shelve.StringIO(self.dict[key])
		try:
			return shelve.Unpickler(f).load()
		except EOFError:
			# apparently file is truncated; delete it and raise
			# and exception
			del self.dict[key]
			raise KeyError("Corrupted or truncated file for key %s "
				"(bad file has been deleted)" % (`key`,))

	def __setitem__(self, key, value):
		f = shelve.StringIO()
		p = shelve.Pickler(f,1)
		p.dump(value)
		self.dict[key] = f.getvalue()

	def close(self):
		if hasattr(self,'dict') and hasattr(self.dict,'close'):
			try:
				self.dict.close()
			except:
				pass
		self.dict = 0

class DirectoryShelf(Shelf):
	"""Shelf implementation using the directory db interface.

	This is initialized with the filename for the dirdbm database.
	"""

	def __init__(self, filename, flag='c'):
		Shelf.__init__(self, dirdbm.open(filename, flag))

def open(filename, flag='c'):
	"""Open a persistent dictionary for reading and writing.

	Argument is the filename for the dirdbm database.
	"""
	
	return DirectoryShelf(filename, flag)