Reference value of expression inside list comprehension in Python?

Question

If I have a list comprehension like

[mymap.get(x, None) for x in oldlist if mymap.get(x,None)]

Is there a way to do mymap.get(x,None) only once here?

I imagine something like

[y for x in oldlist if mymap.get(x,None) as y]

but currently this is a SyntaxError in py 2.x. I would like to be able to reference the resulting values of either the "expression" of list comprehension or from the "list_if" part of it.

I've also tried

[_ for x in oldlist if mymap.get(x,None)]

but that's a NameError, I guess _ being only some interpreter feature on lines.

edit

Is there a way to reference this temporary/anonymous/unnamed variable somehow, without re-iterating the list?

Answer 1

[y for y in (mymap.get(x, None) for x in oldlist) if y]

Answer 2

filter(None, (mymap.get(x, None) for x in oldlist))

or if it suits your fancy the equivalent code using bool instead

filter(bool, (mymap.get(x, None) for x in oldlist))

And to answer your question, there's no way to reference the output function from the predicate.