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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.

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    github.com/python/cpython/blob/… Commented Mar 1, 2018 at 1:14
  • Thanks, this helps a lot. Commented Mar 1, 2018 at 1:20
  • The standard dict in Python 3.6 is also ordered, but it's much more efficient. Commented Mar 1, 2018 at 3:47

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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.
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I guess there's a bit more overhead when using OrderedDict than from the normal dict.

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