code: def open(self, path, mode='r'):
          
  
          entry = self.find(path)
          if entry is None:
              if mode == 'r':
                  raise ValueError("stream does not exists: %s" % path)
              entry = self.create_dir_entry(path, 'stream', None)
  
          else:
              if not entry.isfile():
                  raise ValueError("can only open stream type DirEntry's")
  
              if mode == 'w':
                  logging.debug("stream: %s exists, overwriting" % path)
                  self.free_fat_chain(entry.sector_id, entry.byte_size < self.min_stream_max_size)
                  entry.sector_id = None
                  entry.byte_size = 0
                  entry.class_id = None
              elif mode == 'rw':
                  pass
  
          s = Stream(self, entry, mode)
          return s
docs: Open stream, returning ``Stream`` object