:func:`map` and :func:`filter` return iterators.If you really need a list and the input sequences are all of equal length, a quick fix is to wrap :func:`map` in :func:`list`, e.g. ``list(map(...))``, but a better fix is often to use a list comprehension (especially when the original code uses :keyword:`lambda`), or rewriting the code so it doesn't need a list at all.Particularly tricky is :func:`map` invoked for the side effects of the function; the correct transformation is to use a regular :keyword:`for` loop (since creating a list would just be wasteful).