wsgiref报错AttributeError: 'NoneType' object has no attribute 'split'

from wsgiref.simple_server import make_server

def simple_app(environ, start_response):
    """Simplest possible application object"""
    status = '200 OK'
    response_headers = [('Content-type', 'text/plain')]
    start_response(status, response_headers)
    return ['Hello world!\n']

if __name__ == '__main__':
    httpd = make_server('127.0.0.1', 8000, simple_app)
    address = httpd.socket.getsockname()
    print ('http://{0}:{1}/'.format(*address))
    httpd.serve_forever()

在尝试用python自带的wsgiref模块写框架时，用python3运行以上代码时，发现服务程序可以启动，但是浏览器打开127.0.0.1:8000时，浏览器显示未有数据返回，终端报错：

127.0.0.1 - - [02/Apr/2020 08:56:02] "GET / HTTP/1.1" 200 0
Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 266, in write
    "write() argument must be a bytes instance"
AssertionError: write() argument must be a bytes instance
127.0.0.1 - - [02/Apr/2020 08:56:02] "GET / HTTP/1.1" 500 59
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 38708)
Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 266, in write
    "write() argument must be a bytes instance"
AssertionError: write() argument must be a bytes instance

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 141, in run
    self.handle_error()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 368, in handle_error
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 274, in write
    self.send_headers()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 331, in send_headers
    if not self.origin_server or self.client_is_modern():
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 344, in client_is_modern
    return self.environ['SERVER_PROTOCOL'].upper() != 'HTTP/0.9'
TypeError: 'NoneType' object is not subscriptable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/socketserver.py", line 320, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/usr/lib/python3.6/socketserver.py", line 351, in process_request
    self.finish_request(request, client_address)
  File "/usr/lib/python3.6/socketserver.py", line 364, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.6/socketserver.py", line 724, in __init__
    self.handle()
  File "/usr/lib/python3.6/wsgiref/simple_server.py", line 133, in handle
    handler.run(self.server.get_app())
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 144, in run
    self.close()
  File "/usr/lib/python3.6/wsgiref/simple_server.py", line 35, in close
    self.status.split(' ',1)[0], self.bytes_sent
AttributeError: 'NoneType' object has no attribute 'split'
----------------------------------------
127.0.0.1 - - [02/Apr/2020 08:57:02] "GET / HTTP/1.1" 200 0
Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 266, in write
    "write() argument must be a bytes instance"
AssertionError: write() argument must be a bytes instance
127.0.0.1 - - [02/Apr/2020 08:57:02] "GET / HTTP/1.1" 500 59
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 38712)
Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 138, in run
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 266, in write
    "write() argument must be a bytes instance"
AssertionError: write() argument must be a bytes instance

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 141, in run
    self.handle_error()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 368, in handle_error
    self.finish_response()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 274, in write
    self.send_headers()
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 331, in send_headers
    if not self.origin_server or self.client_is_modern():
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 344, in client_is_modern
    return self.environ['SERVER_PROTOCOL'].upper() != 'HTTP/0.9'
TypeError: 'NoneType' object is not subscriptable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/socketserver.py", line 320, in _handle_request_noblock
    self.process_request(request, client_address)
  File "/usr/lib/python3.6/socketserver.py", line 351, in process_request
    self.finish_request(request, client_address)
  File "/usr/lib/python3.6/socketserver.py", line 364, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.6/socketserver.py", line 724, in __init__
    self.handle()
  File "/usr/lib/python3.6/wsgiref/simple_server.py", line 133, in handle
    handler.run(self.server.get_app())
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 144, in run
    self.close()
  File "/usr/lib/python3.6/wsgiref/simple_server.py", line 35, in close
    self.status.split(' ',1)[0], self.bytes_sent
AttributeError: 'NoneType' object has no attribute 'split'
----------------------------------------

查看最后一行报错无法确认原因，向上翻，发现：

File "/usr/lib/python3.6/wsgiref/handlers.py", line 180, in finish_response
    self.write(data)
  File "/usr/lib/python3.6/wsgiref/handlers.py", line 266, in write
    "write() argument must be a bytes instance"
AssertionError: write() argument must be a bytes instance

确认问题出现在wsgiref模块的handlers.py的180行，查看此write方法：

    def finish_response(self):
        """Send any iterable data, then close self and the iterable

        Subclasses intended for use in asynchronous servers will
        want to redefine this method, such that it sets up callbacks
        in the event loop to iterate over the data, and to call
        'self.close()' once the response is finished.
        """
        try:
            if not self.result_is_file() or not self.sendfile():
                for data in self.result:		
                    self.write(data)
                self.finish_content()
        finally:
            self.close()

    def write(self, data):
        """'write()' callable as specified by PEP 3333"""

        assert type(data) is bytes, \
            "write() argument must be a bytes instance"

        if not self.status:
            raise AssertionError("write() before start_response()")

        elif not self.headers_sent:
            # Before the first output, send the stored headers
            self.bytes_sent = len(data)    # make sure we know content-length
            self.send_headers()
        else:
            self.bytes_sent += len(data)

        # XXX check Content-Length and truncate if too many bytes written?
        self._write(data)
        self._flush()

发现要求data为bytes类型，报错显示我们传入的data非bytes类型，所以，找到刚才的180行代码：修改为

self.write(data.encode())

encode() 方法为字符串类型（str）提供的方法，用于将 str 类型转换成 bytes 类型，这个过程也称为“编码”。

修改保存，重新启动服务器，浏览器可以正常使用