Wsgiref Error: AttributeError: 'NoneType' object has no attribute 'split'

DemoApp is called; The return value of DemoApp.__init__ is used.

DemoApp.__init__ returns nothing (You can't return anything in constructor).

Try following instead of DemoApp class:

def DemoApp(environ, start_response):
    response_headers = [('Content-type','text/plain')]
    start_response('200 OK', response_headers)
    return ["Hello World"]

Using class (Use __call__ instead of __iter__):

from wsgiref.simple_server import make_server

class DemoApp:
    def __call__(self, environ, start_response):
        response_headers = [('Content-type','text/plain')]
        start_response('200 OK', response_headers)
        return ["Hello World"]


if __name__ == '__main__':
    httpd = make_server('', 1000, DemoApp()) # Don't forget instantiate a class.
    #                                    ^^
    print("Serving on port 1000")
    httpd.serve_forever()

You should encode the returned body to utf-8

return ["Hello World".encode("utf-8")]

This code works fine with me, I am using Python 3.3.3:

from wsgiref.simple_server import make_server


def app(env, start_response):
    body = "Hello"
    status = "200 OK"
    headers = [("Content-Type", "text/plain; charset=utf-8")]
    start_response(status, headers)
    return [body.encode("utf-8")]

port = 9080
httpd = make_server("localhost", port, app)
print("Server started on port: ", port)
httpd.serve_forever()

How about this, you need to yield the output than returning it.

from wsgiref.simple_server import make_server

class DemoApp:

    def __init__(self, environ, start_response):
        self.environ = environ
        self.start = start_response

    def __iter__(self):
        status = '200 OK'
        response_headers = [('Content-type', 'text/plain')]
        self.start(status, response_headers)
        yield 'Hello world!'


if __name__ == '__main__':
    httpd = make_server('', 1000, DemoApp)
    print("Serving HTTP on port 1000...")
    httpd.serve_forever()