Message 286162 - Python tracker

Serhiy Storchaka: "The assertion was valid while all keywords did came from a constant keywords tuple in CALL_FUNCTION_KW. But if the FASTCALL protocol is extended for var-keyword arguments, keywords can be arbitrary and the assertion can fail. The assertion on the next line can fail too."

Oh right, I didn't notice that. Since it's an issue of the tp_fastnew/tp_fastinit patch, I replied there:
http://bugs.python.org/issue29358#msg286161