OrderedDict和dict区别

Some differences from dict still remain:

• The regular dict was designed to be very good at mapping operations. Tracking insertion order was secondary.
• The OrderedDict was designed to be good at reordering operations. Space efficiency, iteration speed, and the performance of update operations were secondary.
• The OrderedDict algorithm can handle frequent reordering operations better than dict. As shown in the recipes below, this makes it suitable for implementing various kinds of LRU caches.
• The equality operation for OrderedDict checks for matching order.
  A regular dict can emulate the order sensitive equality test with p==q and all==k2 for k1,k2 in zip(p,q)).
• The popitem() method of OrderedDict has a different signature. It accepts an optional argument to specify which item is popped.
  A regular dict can emulate OrderedDict’s od.popitem(last=True) with d.popitem() which is guaranteed to pop the rightmost (last) item.
  A regular dict can emulate OrderedDict’s od.popitem(last=False) with (k:=next(iter(d)),d.pop(k)) which will return and remove the leftmost (first) item if it exists.
• OrderedDict has a move_to_end() method to efficiently reposition an element to an endpoint.
  A regular dict can emulate OrderedDict’s od.move_to_end(k,last=True) with d[k]=d.pop(k) which will move the key and its associated value to the rightmost (last) position.
  A regular dict does not have an efficient equivalent for OrderedDict’s od.move_to_end(k,last=False) which moves the key and its associated value to the leftmost (first) position.
• Until Python 3.8, dict lacked a __reversed__() method.

参考链接：
dict-ordereddict-difference