I'd desugar it like this:

    >>> lookup = {}
    >>> for (x, lookup[x]) in ('ab', 'cd', 'ef'):
    ...     pass
    ... 
    >>> lookup
    {'a': 'b', 'c': 'd', 'e': 'f'}

This makes is much more clear that there is just a double assignment, and that comprehension are pretty close to regular `for` statement.

(this was a great example btw -- I write python3 a lot, and I was staring at it for a long time before Icould figure it out)