code: def build_usage_logger(self, log):
          '''Return a method that logs progress/mem usage.'''
          def _log_usage():
              log.debug("{}mb peak memory", peak_memory())
              log.debug("{} pending alignment pairs; {} peak pairs",
                        self.pending_pair_count,
                        self.pending_pair_peak_count)
          return _log_usagf build_usage_logger(self, log):
          '''Return a method that logs progress/mem usage.'''
          def _log_usage():
              log.debug("{}mb peak memory", peak_memory())
              log.debug("{} pending alignment pairs; {} peak pairs",
                        self.pending_pair_count,
                        self.pending_pair_peak_count)
          return _log_usage
docs: Return a method that logs progress/mem usage.