fix circular reference, this will introduce memory leaks

olefile/olefile.py

@@ -278,6 +278,7 @@
 
 import io
 import sys
+import weakref
 import struct, array, os.path, datetime, logging
 
 #=== COMPATIBILITY WORKAROUNDS ================================================
@@ -1901,14 +1902,14 @@ def _open(self, start, size = UNKNOWN_SIZE, force_FAT=False):
  return OleStream(fp=self.ministream, sect=start, size=size,
  offset=0, sectorsize=self.minisectorsize,
  fat=self.minifat, filesize=self.ministream.size,
- olefileio=self)
+ olefileio=weakref.ref(self))
  else:
  # standard stream
  return OleStream(fp=self.fp, sect=start, size=size,
  offset=self.sectorsize,
  sectorsize=self.sectorsize, fat=self.fat,
  filesize=self._filesize,
- olefileio=self)
+ olefileio=weakref.ref(self))
 
 
  def _list(self, files, prefix, node, streams=True, storages=False):