from wsgiref.simple_server import make_server


def demo_app(environ, start_response):
    from io import StringIO
    stdout = StringIO()
    print("Hello world!", file=stdout)
    print(file=stdout)
    h = sorted(environ.items())
    for k, v in h:
        print(k, '=', repr(v), file=stdout)
    start_response("200 OK", [('Content-Type', 'text/plain; charset=utf-8')])
    return [stdout.getvalue().encode("utf-8")]


def start_wsgi():
    httpd = make_server('', 8000, demo_app)
    sa = httpd.socket.getsockname()
    print("Serving HTTP on", sa[0], "port", sa[1], "...")
    httpd.serve_forever()

def logger(fn):
    def wrapper():
        print('%s starts to executing' % fn.__name__)
        fn()
        print('%s finished executing' % fn.__name__)
    return wrapper


@logger
def hello():
    print('Hello world!')
##
hello starts to executing
Hello world!
hello finished executing