Specialized `match_keys` for exact dictionary type

Feature or enhancement

I think it's probably worthwhile to write a specialized version of match_keys (for structural pattern matching of mappings) for exact dictionary types

Pitch

The most common mapping type is almost certainly the built-in dict. The match_keys function in ceval.c could be specialized to handle this type. Doing so would allow you to skip the dummy object, and replace the get call with PyDict_GetItemWithError. I don't think this should change the observable behaviour at all for exact dict

I'm in the process of reimplementing structural pattern matching on Cython, and this change gives ~2x optimization of some microbenchmarks.

If this change is deemed desirable I'm happy to implement it myself.

Previous discussion

Not aware of any

从 ceval.c 中的 match_keys 开始，检查 structural pattern matching 当前如何处理 mapping 键和精确的 dict 类型。当精确的 dict 使用专用路径，同时不改变可观察行为（包括现有的查找语义）时，修改就完成了；如果有可用的相关微基准，请进行比较。