Python 3 was slower than the preceding Python 2.x version, I believe; it's getting more difficult to find sources now (it's been a while) but there's plenty of resources that showed Python 3 had performance regressions.
Python 3 is the most striking example but it's unfortunately common in Python. Generators were originally slower than list comps, so after their introduction some modules got slower as they switched internally. super was slower than explicit parent calls, and some modules switched even if they didn't immediately need the fancier MRO. True and False were slightly faster when they were alternate names for 1/0 rather than a different type due to various fast-paths for int handling. I think before 2.3 old-style classes were still faster than new-style classes in some cases, but my memory is pretty fuzzy.
Python 3 was slower than the preceding Python 2.x version, I believe; it's getting more difficult to find sources now (it's been a while) but there's plenty of resources that showed Python 3 had performance regressions.