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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 next(self):
 """Returns a handler to the next file. Non existent files will be logged and skipped. The file might have been removed after input splitting. Returns: The next input from this input reader in the form of a cloudstorage ReadBuffer that supports a File-like interface (read, readline, seek, tell, and close). An error may be raised if the file can not be opened. Raises: StopIteration: The list of files has been exhausted. """

    options = {}
    if self._buffer_size:
      options["read_buffer_size"] = self._buffer_size
    if self._account_id:
      options["_account_id"] = self._account_id
    while True:
      filename = self._next_file()
      if filename is None:
        raise StopIteration()
      if (self._path_filter and
          not self._path_filter.accept(self._slice_ctx, filename)):
        continue
      try:
        start_time = time.time()
        handle = cloudstorage.open(filename, **options)
        self._slice_ctx.incr(self.COUNTER_IO_READ_MSEC,
                             int(time.time() - start_time) * 1000)
        self._slice_ctx.incr(self.COUNTER_FILE_READ)
        return handle
      except cloudstorage.NotFoundError:
        logging.warning("File %s may have been removed. Skipping file.",
                        filename)
        self._slice_ctx.incr(self.COUNTER_FILE_MISSING)