code: def spm_hrf(tr, oversampling=50, time_length=32., onset=0.):
      
      return _gamma_difference_hrf(tr, oversampling, time_length, onset)
docs: Implementation of the SPM hrf model
  
      Parameters
      ----------
      tr : float
          scan repeat time, in seconds
  
      oversampling : int, optional
          temporal oversampling factor
  
      time_length : float, optional
          hrf kernel length, in seconds
  
      onset : float, optional
          hrf onset time, in seconds
  
      Returns
      -------
      hrf: array of shape(length / tr * oversampling, dtype=float)
           hrf sampling on the oversampled time grid