How does OrderedDict keep things in Order in Python

Question

I'm curious as to how OrderedDict from the collections library keeps key/pair order? I looked around online and couldn't find an answer.

Answer 1

From the source code, it appears to be implemented as a dict with a doubly linked list of keys for ordering, as well as another dict that maps keys to their position in the list.

• Insertion just adds to the end of the list.
• Deletion uses the second dict to remove an element from the list.
• Iteration iterates over the linked list.