This solution relies on operators throwing a TypeError to check if the arguments are numbers. Deferring calculation using lambda functions would result in calculator('a','b','+') incorrectly returning "ab" instead of "unknown value".

That being said, inputs like calculator(3,0,'+') would result in a ZeroDivisionError being thrown instead of the correct answer of 3.

You should use lambda functions as the values in the dict so you don't precalculate all 4 ops.

It is flawed. The last of the 3 test cases (for Julia at least, not sure if it's the same for other languages) does require you to use the logic in the description.