def startPrefixMapping(self, prefix, uri):

        self.prefixMap = nscontext(self.prefixMap)
        self.prefixMap[uri] = prefix

        # Ignore Nevow's namespace, we'll replace those during parsing.
        if uri == nevow.namespace:
            return

        # Add to a list that will be applied once we have the element.
        if prefix is None:
            self.xmlnsAttrs.append(('xmlns',uri))
        else:
            self.xmlnsAttrs.append((prefix%'xmlns:%s',uri))
dataset/ETHPy150Open twisted/nevow/nevow/flat/flatsax.py/ToStan.startPrefixMapping/swapped operands of `%`