def join_header_words(lists):
    """Do the inverse (almost) of the conversion done by split_header_words.

    Takes a list of lists of (key, value) pairs and produces a single header
    value.  Attribute values are quoted if needed.

    >>> join_header_words([[("text/plain", None), ("charset", "iso-8859/1")]])
    'text/plain; charset="iso-8859/1"'
    >>> join_header_words([[("text/plain", None)], [("charset", "iso-8859/1")]])
    'text/plain, charset="iso-8859/1"'

    """
    headers = []
    for pairs in lists:
        attr = []
        for k, v in pairs:
            if v is not None:
                if not re.search(r"^\w+$", v):
                    v = HEADER_JOIN_ESCAPE_RE.sub(r"\\\1", v)  # escape " and \
                    v = '"%s"' % v
                k = "%s=%s" % (k, v)
            attr.append(k)
        if attr: headers.append("; ".join(attr))
    return ", ".join(headers)
Do the inverse (almost) of the conversion done by split_header_words.

    Takes a list of lists of (key, value) pairs and produces a single header
    value.  Attribute values are quoted if needed.

    >>> join_header_words([[("text/plain", None), ("charset", "iso-8859/1")]])
    'text/plain; charset="iso-8859/1"'
    >>> join_header_words([[("text/plain", None)], [("charset", "iso-8859/1")]])
    'text/plain, charset="iso-8859/1"'