I find Python's list comprehensions unusable because they're backwards from how I'd expect. Thankfully in Scala the syntax is almost exactly the same; you write

    for {
      a <- list1
      b <- list2
    } { do something}

for an imperative for loop, and

    for {
      a <- whatever1
      b <- whatever2
    } yield { ... }

for the general comprehension. In Python you have to put the equivalent of the yield right at the start, which is just so different from how everything else in the language works.