code: def select_waveform_generator(approximant):
      
  
      # check if frequency-domain CBC waveform
      if approximant in waveform.fd_approximants():
          return FDomainCBCGenerator
  
      # check if time-domain CBC waveform
      elif approximant in waveform.td_approximants():
          return TDomainCBCGenerator
  
      # check if frequency-domain ringdown waveform
      elif approximant in ringdown.ringdown_fd_approximants:
          if approximant == 'FdQNMfromFinalMassSpin':
              return FDomainMassSpinRingdownGenerator
          elif approximant == 'FdQNMfromFreqTau':
              return FDomainFreqTauRingdownGenerator
  
      elif approximant in ringdown.ringdown_td_approximants:
          if approximant == 'TdQNMfromFinalMassSpin':
              return TDomainMassSpinRingdownGenerator
          elif approximant == 'TdQNMfromFreqTau':
              return TDomainFreqTauRingdownGenerator
  
      # otherwise waveform approximant is not supported
      else:
          raise ValueError("%s is not a valid approximant." % approximant)
docs: Returns the single-IFO generator for the approximant.
  
      Parameters
      ----------
      approximant : str
          Name of waveform approximant. Valid names can be found using
          ``pycbc.waveform`` methods.
  
      Returns
      -------
      generator : (PyCBC generator instance)
          A waveform generator object.
  
      Examples
      --------
      Get a list of available approximants:
      >>> from pycbc import waveform
      >>> waveform.fd_approximants()
      >>> waveform.td_approximants()
      >>> from pycbc.waveform import ringdown
      >>> ringdown.ringdown_fd_approximants.keys()
  
      Get generator object:
      >>> from pycbc.waveform.generator import select_waveform_generator
      >>> select_waveform_generator(waveform.fd_approximants()[0])