code: def apply_smoothing(self, smooth_fwhm):
          
          if smooth_fwhm <= 0:
              return
  
          old_smooth_fwhm   = self._smooth_fwhm
          self._smooth_fwhm = smooth_fwhm
          try:
              data = self.get_data(smoothed=True, masked=True, safe_copy=True)
          except ValueError as ve:
              self._smooth_fwhm = old_smooth_fwhm
              raise
          else:
              self._smooth_fwhm = smooth_fwhm
              return data
docs: Set self._smooth_fwhm and then smooths the data.
          See boyle.nifti.smooth.smooth_imgs.
  
          Returns
          -------
          the smoothed data deepcopied.