Most of those tools don't like IRI like: http://müller.de/ or the most famous http://☃.net (http://xn--n3h.net/) and that's a shame! Just like many URL shorteners…

For example, Django do it wrong (even though I tried: https://code.djangoproject.com/ticket/11522):

    >>> print(django.VERSION)
    (1, 3, 1, 'final', 0)
    >>> print(django.http.HttpResponseRedirect(u"http://müller.de))
    Content-Type: text/html; charset=utf-8
    Location: http://m%C3%BCller.de

While werkzeug is good!

    >>> print(werkzeug.__version__)
    0.8.1
    >>> werkzeug.redirect(u"http://müller.de).headers
    Headers([('Content-Type', 'text/html; charset=utf-8'), 
             ('Content-Length', '247'),
             ('Location', 'http://xn--mller-kva.de)]