Return elements in xml files which match with the tag name and the specific attribute

            :param tag_name: a string which specify the tag name
            :param attribute: a string which specify the attribute

def get_elements(self, tag_name, attribute):
        """
            Return elements in xml files which match with the tag name and the specific attribute

            :param tag_name: a string which specify the tag name
            :param attribute: a string which specify the attribute
        """
        l = []
        for i in self.xml:
            for item in self.xml[i].getElementsByTagName(tag_name):
                value = item.getAttributeNS(NS_ANDROID_URI, attribute)
                value = self.format_value(value)

                l.append(str(value))
        return l