Removing dictionary-keys not in a set?

[Tim N. van der Leeuw]

Hi Aahz,

The problem with using the builtin set operations is, that the
dictionary keys don't represent a set, so you can't directly create a
new dictionary using set methods.

So I'm looking for what's a concise way to update a dictionary, or
create a new dictionary, using basically an intersection method.

(I'm using Python 2.4.1 so I do have convenient builtin set operations
available)

In my taste, using generator expressions with conditions actually
doesn't look very readable; it hides the set-membership test under the
syntactic clutter.
(I don't mind generator expressions in principle, but I do feel that
here they clutter up the intent of the code)

cheers,

--Tim