@gen.engine
  def FetchExistingFromS3(self, callback):
    contents = yield gen.Task(self._logs_store.Get, self._s3_filename, must_exist=False)
    if contents is not None:
      logging.info('Fetched %d bytes from existing S3 merged log file %s' % (len(contents), self._s3_filename))
      self._output.write(contents)
      self._output.flush()
      self._needs_separator = True
    callback()
Returns True if adding filters to this instance is still possible.
dataset/ETHPy150Open viewfinderco/viewfinder/backend/logs/log_merger.py/LocalLogMerge.FetchExistingFromS3--crossover with--dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Django-1.6.10/django/db/models/sql/query.py/Query.can_filter