Map and filter don't actually consume anything until they're used later, they produce iterables. So if you pulled them into their own lines they wouldn't consume (much) extra memory. Taking the original:

  min(map(some_op, filter(some_filter, bar.baz()))).foo()

An alternative is also to use a generator comprehension that's identical to the inner part (in effect):

  min(some_op(item) for item in bar.baz() if some_filter(item)).foo()

Which could still be pulled out to a pair of lines for clarity:

  items = (some_op(item) for item in bar.baz() if some_filter(item)) # or some better name given a context
  min(items).foo()