@cedrickrier So in the first one you're feeding update a generator, but in the second one you're feeding it another dictionary? If so, it makes sense that the second one takes much longer, as you're building the entire dictionary twice.
@cedrickrier Oh, MICROseconds -- I missed that!
Interesting. I'd think the dictionary would need to create all of the tuples (or some equivalent key-value pairs) anyway. Maybe the behind-the-scenes data structure storing a pair in a dictionary is more efficient than a tuple, because it knows it contains exactly two items.