code: def get_function_spec(name):
      
      if not hasattr(get_function_spec, 'fndict'):
          modelfile = os.path.join('$FERMIPY_ROOT',
                                   'data', 'models.yaml')
          modelfile = os.path.expandvars(modelfile)
          get_function_spec.fndict = yaml.load(open(modelfile))
  
      if not name in get_function_spec.fndict.keys():
          raise Exception('Invalid Function Name: %s' % name)
  
      return get_function_spec.fndict[name]
docs: Return a dictionary with the specification of a function:
      parameter names and defaults (value, bounds, scale, etc.).
  
      Returns
      -------
      par_names : list
          List of parameter names for this function.
  
      norm_par : str
          Name of normalization parameter.
  
      default : dict
          Parameter defaults dictionary.