code: def _create_morlet(options, s_freq):
      
      wavelets = []
      foi = options.pop('foi')
      for f in foi:
          wavelets.append(morlet(f, s_freq, **options))
  
      return wavelets
docs: Create morlet wavelets, with scipy.signal doing the actual computation.
  
      Parameters
      ----------
      foi : ndarray or list or tuple
          vector with frequency of interest
      s_freq : int or float
          sampling frequency of the data
      options : dict
          with 'M_in_s' (duration of the wavelet in seconds) and 'w' (Omega0)
  
      Returns
      -------
      ndarray
          nFreq X nSamples matrix containing the complex Morlet wavelets.