It needs to be [bar(foo(y)) for y in (z for z in stuff if foo(z))] (etc.) though, since `bar` takes as input the output of `foo`. This leads to the object

It needs to be [bar(foo(y)) for y in (z for z in stuff if foo(z))] (etc.) though, since `bar` takes as input the output of `foo`. This leads to the objectionable duplicate calls to `foo`, hence the new assignment expressions. I like Dunnorandom's [bar(x) for x in map(foo, stuff) if x] best for a correct result using existing syntax, or [bar(x) for y in (foo(x) for x in stuff) if y] if you don't like `map`.