code: def get_coef_indices(self, i=-1):
          
          if i == -1:
              return list(range(self.n_coefs))
  
          if i >= len(self._terms):
              raise ValueError('requested {}th term, but found only {} terms'\
                              .format(i, len(self._terms)))
  
          start = 0
          for term in self._terms[:i]:
              start += term.n_coefs
          stop = start + self._terms[i].n_coefs
          return list(range(start, stop))
docs: get the indices for the coefficients of a term in the term list
  
          Parameters
          ---------
          i : int
              by default `int=-1`, meaning that coefficient indices are returned
              for all terms in the term list
  
          Returns
          -------
          list of integers