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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add(self, observableElement):
 """ add an observable element :param str observableElement: the name of the observable element :raises RuntimeError: if element name already exist in the store """

        if observableElement not in self._observables:
            self._observables.append(observableElement)
        else:
            raise RuntimeError(
                "{0} is already an observable element"
                .format(observableElement))