old_contents: __all__ = ['fftshift', 'ifftshift', 'fftfreq', 'rfftfreq']
  
  from numpy import array
  from numpy.fft.helper import fftshift, ifftshift, fftfreq
  
  def rfftfreq(n, d=1.0):
      """DFT sample frequencies (for usage with rfft, irfft).
  
      The returned float array contains the frequency bins in
      cycles/unit (with zero at the start) given a window length n and a
      sample spacing d::
  
        f = [0,1,1,2,2,...,n/2-1,n/2-1,n/2]/(d*n)   if n is even
        f = [0,1,1,2,2,...,n/2-1,n/2-1,n/2,n/2]/(d*n)   if n is odd
      """
      if not isinstance(n, int) or n < 0:
          raise ValueError("n = %s is not valid.  n must be a nonnegative integer." % n)
      return (array(range(1,n+1),dtype=int)//2)/float(n*d)
  
new_contents: __all__ = ['fftshift', 'ifftshift', 'fftfreq', 'rfftfreq']
  
  from numpy import arange
  from numpy.fft.helper import fftshift, ifftshift, fftfreq
  
  def rfftfreq(n, d=1.0):
      """DFT sample frequencies (for usage with rfft, irfft).
  
      The returned float array contains the frequency bins in
      cycles/unit (with zero at the start) given a window length `n` and a
      sample spacing `d`::
  
        f = [0,1,1,2,2,...,n/2-1,n/2-1,n/2]/(d*n)   if n is even
        f = [0,1,1,2,2,...,n/2-1,n/2-1,n/2,n/2]/(d*n)   if n is odd
  
      Parameters
      ----------
      n : int
          Window length.
      d : scalar, optional
          Sample spacing. Default is 1.
  
      Returns
      -------
      out : ndarray
          The array of length `n`, containing the sample frequencies.
  
      Examples
      --------
      >>> from scipy import fftpack
      >>> sig = np.array([-2, 8, 6, 4, 1, 0, 3, 5], dtype=float)
      >>> sig_fft = fftpack.rfft(sig)
      >>> n = sig_fft.size
      >>> timestep = 0.1
      >>> freq = fftpack.rfftfreq(n, d=timestep)
      >>> freq
      array([ 0.  ,  1.25,  1.25,  2.5 ,  2.5 ,  3.75,  3.75,  5.  ])
  
      """
      if not isinstance(n, int) or n < 0:
          raise ValueError("n = %s is not valid.  n must be a nonnegative integer." % n)
  
      return (arange(1, n + 1, dtype=int) // 2) / float(n * d)
  
subject: add parameters, returns and an example to fftpack.rfftfreq docstring.