private: set the omitted jco attribute

def __load_omitted_jco(self):
        """private: set the omitted jco attribute
        """
        if self.omitted_par_arg is None:
            raise Exception("ErrVar.__load_omitted: omitted_arg is None")
        if isinstance(self.omitted_par_arg,str):
            if self.omitted_par_arg in self.jco.col_names:
                # need to access attribute directly, not view of attribute
                self.__omitted_jco = \
                    self._LinearAnalysis__jco.extract(
                        col_names=self.omitted_par_arg)
            else:
                # must be a filename
                self.__omitted_jco = self.__fromfile(self.omitted_par_arg)
        # if the arg is an already instantiated Matrix (or jco) object
        elif isinstance(self.omitted_par_arg,Jco) or \
                isinstance(self.omitted_par_arg,Matrix):
            self.__omitted_jco = \
                Jco(x=self.omitted_par_arg.newx(),
                          row_names=self.omitted_par_arg.row_names,
                          col_names=self.omitted_par_arg.col_names)
        # if it is a list, then it must be a list
        # of parameter names in self.jco
        elif isinstance(self.omitted_par_arg,list):
            for arg in self.omitted_par_arg:
                if isinstance(arg,str):
                    assert arg in self.jco.col_names,\
                        "ErrVar.__load_omitted_jco: omitted_jco " +\
                        "arg str not in jco par_names: " + str(arg)
            self.__omitted_jco = \
                self._LinearAnalysis__jco.extract(col_names=self.omitted_par_arg)