code: def csd(self, other, fftlength=None, overlap=None, window='hann',
              **kwargs):
          
          return spectral.psd(
              (self, other),
              spectral.csd,
              fftlength=fftlength,
              overlap=overlap,
              window=window,
              **kwargs
          )
docs: Calculate the CSD `FrequencySeries` for two `TimeSeries`
  
          Parameters
          ----------
          other : `TimeSeries`
              the second `TimeSeries` in this CSD calculation
  
          fftlength : `float`
              number of seconds in single FFT, defaults to a single FFT
              covering the full duration
  
          overlap : `float`, optional
              number of seconds of overlap between FFTs, defaults to the
              recommended overlap for the given window (if given), or 0
  
          window : `str`, `numpy.ndarray`, optional
              window function to apply to timeseries prior to FFT,
              see :func:`scipy.signal.get_window` for details on acceptable
              formats
  
          Returns
          -------
          csd :  `~gwpy.frequencyseries.FrequencySeries`
              a data series containing the CSD.