Oh, yes, of course you're right, I didn't see that until now - did I say already, that I hate Python's list comprehensions or everything not totally simple?.
Technically that's a dict comprehension, not a list comprehension (though they are pretty much the same). The old style, before they existed, was to create a list of 2-tuples (key/value pairs) in a list comprehension and pass that to dict().
So that needs reduce: