


Detailed introduction to implementing ordered dictionary in Python (with code)
This article brings you a detailed introduction to the implementation of ordered dictionaries in python (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
How to implement a dictionary that can save the insertion order of key values?
There are two main points:
A doubly linked list, used to record the insertion order of key values in the dictionary
A mapping between keys and linked list nodes, mainly used When deleting a key, find the node corresponding to the key
python code implementation
class Link: __slots__ = 'prev', 'next', 'key' class OrderDict: def __init__(self): self.root = Link() self.map = {} self._node_map = {} self.root.next = self.root self.root.prev = self.root def __setitem__(self, key, value): if key in self._node_map: self.map[key] = value else: root = self.root last = root.prev link = Link() link.prev, link.next, link.key = last, root, key last.next = link root.prev = link self._node_map[key] = link self.map[key] = value def __getitem__(self, item): return self.map[item] def __delitem__(self, key): del self.map[key] link = self._node_map.pop(key) link_prev, link_next = link.prev, link.next link_prev.next, link_next.prev = link_next, link_prev link.prev, link.next = None, None def pop(self): """ LIFO :return: """ if not self._node_map: raise KeyError('dict is empty') root = self.root link = root.prev link_prev = link.prev link_prev.next = root root.prev = link_prev link.prev, link.next = None, None self._node_map.pop(link.key) return self.map.pop(link.key) def __iter__(self): root = self.root curr = root.next while curr != root: yield curr.key curr = curr.next def values(self): root = self.root curr = root.next while curr != root: yield self.map[curr.key] curr = curr.next def __str__(self): root = self.root curr = root.next out = [] while curr != root: out.append((curr.key, self.map[curr.key])) curr = curr.next return str(out) if __name__ == '__main__': d = OrderDict() d['a'] = '1' d['b'] = '2' d['c'] = 'c' print(d)
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