code: def cv(self):
      return (
          (self.resid / (1.0 - self.hatmatrix_diag)) ** 2
      ).sum() / self.nobs
  
imports: from statsmodels.compat.python import lrange
  import numpy
  from statsmodels.tools.decorators import cache_readonly
  from statsmodels.regression.linear_model import OLS, GLS, RegressionResults
  from statsmodels.regression.feasible_gls import atleast_2dcols
label_desc: Use image node_id 5 for calling the TheilRegressionResults obj's underlying member method code with example usage: obj.cv() and returns: unknown