I confirmed the cost is negligible. python_startup_no_site ====================== Mean +- std dev: [master] 7.31 ms +- 0.39 ms -> [reverse] 7.41 ms +- 0.44 ms: 1.01x slower (+1%) Mean +- std dev: [master] 7.31 ms +- 0.39 ms -> [register] 7.20 ms +- 0.28 ms: 1.01x faster (-1%) Benchmark hidden because not significant (1): python_startup "register" is "reverse" + following patch: diff --git a/Lib/_collections_abc.py b/Lib/_collections_abc.py index dbe30dff1f..28a7e2586c 100644 --- a/Lib/_collections_abc.py +++ b/Lib/_collections_abc.py @@ -280,6 +280,9 @@ Iterator.register(bytearray_iterator) Iterator.register(dict_keyiterator) Iterator.register(dict_valueiterator) Iterator.register(dict_itemiterator) +Iterator.register(type(iter(reversed({}.keys())))) +Iterator.register(type(iter(reversed({}.values())))) +Iterator.register(type(iter(reversed({}.items())))) Iterator.register(list_iterator) Iterator.register(list_reverseiterator) Iterator.register(range_iterator) @@ -306,6 +309,12 @@ class Reversible(Iterable): return NotImplemented +Reversible.register(dict) +Reversible.register(type({}.keys())) +Reversible.register(type({}.values())) +Reversible.register(type({}.items())) + + class Generator(Iterator): __slots__ = ()