def find_lexer_class_for_filename(_fn, code=None):
    """Get a lexer for a filename.

    If multiple lexers match the filename pattern, use ``analyse_text()`` to
    figure out which one is more appropriate.

    Returns None if not found.
    """
    matches = []
    fn = basename(_fn)
    for modname, name, _, filenames, _ in itervalues(LEXERS):
        for filename in filenames:
            if _fn_matches(fn, filename):
                if name not in _lexer_cache:
                    _load_lexers(modname)
                matches.append((_lexer_cache[name], filename))
    for cls in find_plugin_lexers():
        for filename in cls.filenames:
            if _fn_matches(fn, filename):
                matches.append((cls, filename))

    if sys.version_info > (3,) and isinstance(code, bytes):
        # decode it, since all analyse_text functions expect unicode
        code = guess_decode(code)

    def get_rating(info):
        cls, filename = info
        # explicit patterns get a bonus
        bonus = '*' not in filename and 0.5 or 0
        # The class _always_ defines analyse_text because it's included in
        # the Lexer class.  The default implementation returns None which
        # gets turned into 0.0.  Run scripts/detect_missing_analyse_text.py
        # to find lexers which need it overridden.
        if code:
            return cls.analyse_text(code) + bonus, cls.__name__
        return cls.priority + bonus, cls.__name__

    if matches:
        matches.sort(key=get_rating)
        # print "Possible lexers, after sort:", matches
        return matches[-1][0]
Get a lexer for a filename.

    If multiple lexers match the filename pattern, use ``analyse_text()`` to
    figure out which one is more appropriate.

    Returns None if not found.