Include example of OrderedDict's intransitive __eq__ implementation?

[jab]

The second snippet in cosmologicon/pywat#38 provides an example of such a big WTF in Python that Raymond Hettinger himself even called OrderedDict's intransitive equality a mistake. Any interest in including that here?

[satwikkansal]

Interesting! I'll add it in the next update, or if you like, you can submit a PR for this. Thanks for sharing it 😄

[chris-rands]

Do you have a link for where Raymond said this? I agree the behaviour is not obvious, but it is intended and documented:

Equality tests between OrderedDict objects are order-sensitive and are implemented as list(od1.items())==list(od2.items()). Equality tests between OrderedDict objects and other Mapping objects are order-insensitive like regular dictionaries. This allows OrderedDict objects to be substituted anywhere a regular dictionary is used.

https://docs.python.org/3/library/collections.html#ordereddict-objects

[jab]

This allows OrderedDict objects to be substituted anywhere a regular dictionary is used.

Well, not exactly anywhere, as my od == od2 example from cosmologicon/pywat#38 demonstrates. This imprecision is a bug in the docs. An edge case bug, but still a bug.

[chris-rands]

Interesting thanks, I guess that either way the behaviour would surprise some users. I'm not convinced this is a doc bug, but file it as one if you think so https://bugs.python.org/

[satwikkansal]

Thanks for suggesting this @jab , this was actually one of very few genuine WTFs I've observed. Added in the above commit ^^, feel free to have a look and point out any corrections / missing details.