human
I wrote the below code

    exec_dir = os.path.dirname(os.path.realpath(__file__))
    xml_path = os.path.join(exec_dir, 'data', 'FacebookLocales.xml')
    fb_locales = _build_locale_table(xml_path)
    def default_locale(request):
        "\n                                Guess    an    appropiate    FB    locale    based    on    the    active    Django    locale.\n                                If    the    active    locale    is    available,    it    is    returned.    Otherwise,\n                                it    tries    to    return    another    locale    with    the    same    language.    If    there\n                                isn't    one    avaible,    'en_US'    is    returned.\n                                "
        chosen = 'en_US'
        language = get_language()
        if language:
            locale = to_locale(language)
            (lang, _, reg) = locale.partition('_')
            lang_map = fb_locales.get(lang)
            if (lang_map is not None):
                if (reg in lang_map['regs']):
                    chosen = ((lang + '_') + reg)
                else:
                    chosen = ((lang + '_') + lang_map['default'])
        return chosen
    return default_locale

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

def get_default_locale_callable():