middleware.py

...
    if asbool(static_files):
        # Serve static files
        static_app = StaticURLParser(config['pylons.paths']['static_files'])
        app = Cascade([static_app, app])

    app = CloseConnection(app)
    return app

class CloseConnection:
    def __init__(self, app):
        self.app = app

    def __call__(self, environ, start_response):
        def close_connection_start_response(status, headers, exc_info=None):
            final_headers = []
            for header in headers:
                if header[0].lower() != 'connection':
                    final_headers.append(header)
            final_headers.append(('connection','close'))
            return start_response(status, final_headers, exc_info)
        return self.app(environ, close_connection_start_response)