code: def window_lanczos(N):
      r
      if N ==1:
          return ones(1)
  
      n = linspace(-N/2., N/2., N)
      win = sinc(2*n/(N-1.))
      return win
docs: r"""Lanczos window also known as sinc window.
  
      :param N: window length
  
      .. math:: w(n) = sinc \left(  \frac{2n}{N-1} - 1 \right)
  
      .. plot::
          :width: 80%
          :include-source:
  
          from spectrum import window_visu
          window_visu(64, 'lanczos')
  
      .. seealso:: :func:`create_window`, :class:`Window`