code: def add_into(self, other):
          
          # only handle equal sample rate for now.
          if self.sample_rate != other.sample_rate:
              raise ValueError('Sample rate must be the same')
  
          # Other is disjoint
          if ((other.start_time > self.end_time) or
             (self.start_time > other.end_time)):
              return self.copy()
  
          other = other.copy()
          dt = float((other.start_time - self.start_time) * self.sample_rate)
          if not dt.is_integer():
              diff = (dt - _numpy.floor(dt))
              other.resize(len(other) + (len(other) + 1) % 2 + 1)
              other = other.cyclic_time_shift(diff)
  
          ts = self.copy()
          start = max(other.start_time, self.start_time)
          end = min(other.end_time, self.end_time)
          part = ts.time_slice(start, end)
          part += other.time_slice(start, end)
          return ts
docs: Return the sum of the two time series accounting for the time stamp.
  
          The other vector will be resized and time shifted wiht sub-sample
          precision before adding. This assumes that one can assume zeros
          outside of the original vector range.