code: def deletenode(self, node):
          
          if self._last == node:
              self._last = node.previous
          if self._first == node:
              self._first = node.next
          node.pop()
          del self._index[node.value]
          self._size -= 1
docs: >>> l = DLL()
          >>> l.push(1)
          >>> l
          [1]
          >>> l.size()
          1
          >>> l.deletenode(l._first)
          >>> l
          []
          >>> l.size()
          0
          >>> l._index
          {}
          >>> l._first