code: def setArg(self, namespace, key, value):
          
          assert key is not None
          assert value is not None
          namespace = self._fixNS(namespace)
          # try to ensure that internally it's consistent, at least: str -> str
          if isinstance(value, bytes):
              value = str(value, encoding="utf-8")
          self.args[(namespace, key)] = value
          if not (namespace is BARE_NS):
              self.namespaces.add(namespace)
docs: Set a single argument in this namespace