I am trying to use list comprehension to create a new list of lists of strings in which all strings but the last will be lowercased. This would be the critical line, but it lowercase all strings:

```
[[word.lower() for word in words] for words in lists]

```

If I do this:

```
[[word.lower() for word in words[:-1]] for words in lists]

```

the last element is omitted.

In general, if the list is rather long, is comprehension the best/fastest approach?