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def url_for(*args, **kw):    result = webhelpers.url_for(*args, **kw)    assert result is not None, (        "No route for url_for(%s)" % _format_args(args, kw))    return resultdef _format_args(args, kw):    result = [repr(a) for a in args]    result.extend(['%s=%r' % (name, value) for name, value in sorted(kw.items())])    return ', '.join(result)