human
I wrote the below code

    c = Container(stream.read())
    m = extract_metadata(c.decode())
    def has(x):
        return (m[x] and m[x][0])
    def get(x, single=True):
        ans = m[x]
        if single:
            ans = (clean_xml_chars(ans[0]) if ans else u'')
        else:
            ans = [clean_xml_chars(y) for y in ans]
        return ans
    title = (get(u'title') or _(u'Unknown'))
    authors = (get(u'author', False) or [_(u'Unknown')])
    auth_pat = re.compile(u'([^,]+?)\\s*,\\s+([^,]+)$')
    def fix_author(x):
        if (tweaks[u'author_sort_copy_method'] != u'copy'):
            m = auth_pat.match(x.strip())
            if (m is not None):
                return ((m.group(2) + u'    ') + m.group(1))
        return x
    unique_authors = []
    for f in [fix_author(x) for x in authors]:
        if (f not in unique_authors):
            unique_authors.append(f)
    mi = Metadata(title, unique_authors)
    if has(u'author'):
        mi.author_sort = get(u'author')
    if has(u'ASIN'):
        mi.set_identifier(u'mobi-asin', get(u'ASIN'))
    elif has(u'content_id'):
        mi.set_identifier(u'mobi-asin', get(u'content_id'))
    if has(u'languages'):
        langs = list(filter(None, (canonicalize_lang(x) for x in get(u'languages', False))))
        if langs:
            mi.languages = langs
    if has(u'issue_date'):
        try:
            mi.pubdate = parse_only_date(get(u'issue_date'))
        except Exception:
            pass
    if (has(u'publisher') and (get(u'publisher') != u'Unknown')):
        mi.publisher = get(u'publisher')
    if (read_cover and m[COVER_KEY]):
        try:
            data = base64.standard_b64decode(m[COVER_KEY])
            (fmt, w, h) = identify(bytes(data))
        except Exception:
            (w, h, fmt) = (0, 0, None)
        if (fmt and (w > (-1)) and (h > (-1))):
            mi.cover_data = (fmt, data)
    return mi

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

def read_metadata_kfx(stream, read_cover=True):