[Python-Dev] The current dict is not an "OrderedDict"

[Serhiy Storchaka]

07.11.17 16:56, Steven D'Aprano пише:
> To clarify: if we start with an empty dict, add keys A...D, delete B,
> then add E...H, we could expect:
> 
> {A: 1}
> {A: 1, B: 2}
> {A: 1, B: 2, C: 3}
> {A: 1, B: 2, C: 3, D: 4}
> {D: 4, A: 1, C: 3}  # some arbitrary reordering
> {D: 4, A: 1, C: 3, E: 5}
> {D: 4, A: 1, C: 3, E: 5, F: 6}
> {D: 4, A: 1, C: 3, E: 5, F: 6, G: 7}
> {D: 4, A: 1, C: 3, E: 5, F: 6, G: 7, H: 8}

Rather

{A: 1, D: 4, C: 3}  # move the last item in place of removed
{A: 1, D: 4, C: 3, E: 5}
{A: 1, D: 4, C: 3, E: 5, F: 6}
{A: 1, D: 4, C: 3, E: 5, F: 6, G: 7}
{A: 1, D: 4, C: 3, E: 5, F: 6, G: 7, H: 8}

or

{A: 1, C: 3, D: 4}
{A: 1, E: 5, C: 3, D: 4}  # place the new item in place of removed
{A: 1, E: 5, C: 3, D: 4, F: 6}
{A: 1, E: 5, C: 3, D: 4, F: 6, G: 7}
{A: 1, E: 5, C: 3, D: 4, F: 6, G: 7, H: 8}

or

{A: 1, C: 3, D: 4}
{A: 1, C: 3, D: 4, E: 5}  # add new items at end until fill the array
{A: 1, F: 6, C: 3, D: 4, E: 5}  # and fill holes after that
{A: 1, F: 6, C: 3, D: 4, E: 5, G: 7}  # reallocate the array
{A: 1, F: 6, C: 3, D: 4, E: 5, G: 7, H: 8}

These scenarios are more probably.