code: def pad(self, pad_width, **kwargs):
          
          # format arguments
          kwargs.setdefault('mode', 'constant')
          if isinstance(pad_width, int):
              pad_width = (pad_width,)
          # form pad and view to this type
          new = numpy.pad(self, pad_width, **kwargs).view(type(self))
          # numpy.pad has stripped all metadata, so copy it over
          new.__metadata_finalize__(self)
          new._unit = self.unit
          # finally move the starting index based on the amount of left-padding
          new.x0 -= self.dx * pad_width[0]
          return new
docs: Pad this series to a new size
  
          Parameters
          ----------
          pad_width : `int`, pair of `ints`
              number of samples by which to pad each end of the array.
              Single int to pad both ends by the same amount, or
              (before, after) `tuple` to give uneven padding
          **kwargs
              see :meth:`numpy.pad` for kwarg documentation
  
          Returns
          -------
          series : `Series`
              the padded version of the input
  
          See also
          --------
          numpy.pad
              for details on the underlying functionality