'Close the file stream associated with this corpus view.  This
can be useful if you are worried about running out of file
handles (although the stream should automatically be closed
upon garbage collection of the corpus view).  If the corpus
view is accessed after it is closed, it will be automatically
re-opened.'

def close(self):

    if (self._stream is not None):
        self._stream.close()
    self._stream = None
