参考

• A Do-It-Yourself Framework
• WSGI とPythonでスマートなWebアプリケーション開発を
• 21.4. wsgiref — WSGI ユーティリティとリファレンス実装

paste

def app(environ, start_response):
    start_response('200 OK', [('content-type', 'text/html')])
    return ['Hello world!']

if __name__ == '__main__':
    from paste import httpserver
    httpserver.serve(app, host='127.0.0.1', port='8080')

wsgiref

def app(environ, start_response):
    start_response('200 OK', [('content-type', 'text/html')])
    return ['Hello world!']

if __name__ == '__main__':
    from wsgiref import simple_server
    server = simple_server.make_server('', 8080, app)
    server.serve_forever()

app関数は同じ。