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json.dumps: single circle markers hash lookup #161661
Description
Feature or enhancement
Right now the code does Contains + SetItem for circular reference checks. That can be done as a single hash lookup with PyDict_SetDefault and checking the dictionary size (memory read).
Has this already been discussed elsewhere?
This is a minor feature, which does not need previous discussion elsewhere
Links to previous discussion of this feature:
No response
Activity
picnixz commentedon Nov 9, 2026
How much perf do we gain?
aivarsk commentedon Nov 9, 2026
Updated to
PyDict_SetDefaultReffor a cleaner approach. On a synthetic case with a lot of containers it gives me ~4.5% improvement. For pyperformance it's insignificant 0.x% change.Now with SetDefaultRef I think it's also a cleaner code regardless of perf gains or not.