def make_calls(self, num_calls=1):
        """Adds appropriate sleep to avoid making too many calls.

        Args:
            num_calls: int the number of calls which will be made
        """
        self._cull()
        while self._outstanding_calls + num_calls > self._max_calls_per_second:
            time.sleep(0)  # yield
            self._cull()

        self._call_times.append(self.CallRecord(time=time.time(), num_calls=num_calls))
        self._outstanding_calls += num_calls