DbfilenameShelf instance has no attribute 'writeback'

[warren ali]

Anyone have any idea why this is failing with the following error

class _IndexFile:
"""An _IndexFile is an implementation class that presents a
Sequence and Dictionary interface to a sorted index file."""

def __init__(self, pos, filenameroot):
self.pos = pos
self.file = open(_indexFilePathname(filenameroot), _FILE_OPEN_MODE)
self.offsetLineCache = {}   # Table of (pathname, offset) -> (line,
nextOffset)
self.rewind()
self.shelfname = os.path.join(WNSEARCHDIR, pos + ".pyidx")
try:
import shelve
self.indexCache = shelve.open(self.shelfname, 'r')
except:
pass

Exception exceptions.AttributeError: "DbfilenameShelf instance has no
attribute 'writeback'" in Exception exceptions.AttributeError:
"DbfilenameShelf instance has no attribute 'writeback'" in Exception
exceptions.AttributeError: "DbfilenameShelf instance has no attribute
'writeback'" in Exception exceptions.AttributeError: "DbfilenameShelf
instance has no attribute 'writeback'" in

The code still returns the correct restults but each result come back
with this exception.