Python's dict implementation (in C) is good and the interpreter loop overhead is dwarfed by the dict overhead.
SBCL's implementation is in Lisp and achieves the same speed.
(For the general case of Python speed this benchmark is of course useless, since raw dicts written in C cannot be optimized much. Nevertheless it is sometimes quoted as "evidence" that "Python is almost as fast as C++" ...)
41% of the runtime of my impl. is spent on resizing (19 times) + finally freeing (once) the hashtable.
It's interesting that in your testing unordered_map managed a faster runtime than Python. I've attributed my implementation's defeat to the fact that it uses separate chaining while CPython uses open addressing (+ a bunch of other clever optimizations...), but seeing as unordered_map also uses separate chaining (as mandated by the C++ standard, apparently) and it managed a win in your testing, I'm interested to see how they do things.