code: def _estimate_p_values(self):
          
          if not self._is_fitted:
              raise AttributeError('GAM has not been fitted. Call fit first.')
  
          p_values = []
          for term_i in range(len(self.terms)):
              p_values.append(self._compute_p_value(term_i))
  
          return p_values
docs: estimate the p-values for all features