human
Here's a good function header given the following:
I wrote the below code

    def parse(x):
        try:
            return parse_lang_code(x)
        except ValueError:
            return None
    opf_languages = filter(None, map(parse, opf_languages))
    cc_map = {c.langcode: c.countrycode for c in opf_languages}
    mi_languages = filter(None, map(parse, mi_languages))
    def norm(x):
        lc = x.langcode
        cc = (x.countrycode or cc_map.get(lc, None))
        lc = (lang_as_iso639_1(lc) or lc)
        if cc:
            lc += (u'-' + cc)
        return lc
    return list(map(norm, mi_languages))

What's a good function header?
assistant
#Here's a good function header.

def normalize_languages(opf_languages, mi_languages):