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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def generate(self, callback=None, interval=0):
 """ Hash pieces and report progress to `callback` This method sets ``pieces`` in :attr:`metainfo`\ ``['info']`` when all pieces are hashed successfully. :param callable callback: Callable with signature ``(torrent, filepath, pieces_done, pieces_total)``; if `callback` returns anything else than None, hashing is canceled :param float interval: Minimum number of seconds between calls to `callback` (if 0, `callback` is called once per piece) :raises PathEmptyError: if :attr:`path` contains only empty files/directories :raises PathNotFoundError: if :attr:`path` does not exist :raises ReadError: if :attr:`path` or any file beneath it is not readable :return: ``True`` if all pieces were successfully hashed, ``False`` otherwise """

        if self.path is None:
            raise RuntimeError('generate() called with no path specified')
        elif self.size <= 0:
            raise error.PathEmptyError(self.path)
        elif not os.path.exists(self.path):
            raise error.PathNotFoundError(self.path)

        if callback is not None:
            cancel = lambda *status: callback(*status) is not None
        else:
            cancel = lambda *status: False

        if os.path.isfile(self.path):
            pieces = self._set_pieces_singlefile()
        elif os.path.isdir(self.path):
            pieces = self._set_pieces_multifile()

        # Iterate over hashed pieces and send status information
        last_cb_call = 0
        for filepath,pieces_done,pieces_total in pieces:
            now = time.time()
            if now - last_cb_call >= interval or \
               pieces_done >= pieces_total:
                last_cb_call = now
                if cancel(self, filepath, pieces_done, pieces_total):
                    return False
        return True