code: def check_theta(self):
          
          lower, upper = self.theta_interval
          if (not lower <= self.theta <= upper) or (self.theta in self.invalid_thetas):
              message = 'The computed theta value {} is out of limits for the given {} copula.'
              raise ValueError(message.format(self.theta, self.copula_type.name))
docs: Validate the computed theta against the copula specification.
  
          This method is used to assert the computed theta is in the valid range for the copula.