docs: def replace(self, key, value):
          """Replace the value of the first key-value pair with key *key*.
  
          If the key was not found, the pair is inserted.
          """
          self._find_lt(key)
          node = self._path[0][2]
          if node is self._tail or key < node[0]:
              node = self._create_node(key, value)
              self._insert(node)
          else:
              node[1] = value