Cleans the value before storing it.

        :param:     py_value : <str>

        :return:    <str>

def clean(self, py_value):
        """
        Cleans the value before storing it.

        :param:     py_value : <str>

        :return:    <str>
        """
        try:
            import bleach
            return bleach.clean(py_value, **self.__bleachOptions)
        except ImportError:
            warnings.warn('Unable to clean string column without webhelpers installed.')
            return py_value