def __set_formula(self, formula):
        """
        Sets a formula in this cell.

        Any cell value can be set using this method. Actual formulas must
        start with an equal sign.
        """
        array = ((self._clean_formula(formula),),)
        return self._get_target().setFormulaArray(array)
Sets a formula in this cell.

        Any cell value can be set using this method. Actual formulas must
        start with an equal sign.