import os, sys
enc, esc = sys.getfilesystemencoding(), ‘surrogateescape‘
def unicode_to_wsgi(u):
    # Convert an environment variable to a WSGI "bytes-as-unicode" string
    return u.encode(enc, esc).decode(‘iso-8859-1‘)
def wsgi_to_bytes(s):
    return s.encode(‘iso-8859-1‘)
def run_with_cgi(application):
    # environ参数，里面是HTTP请求的环境变量
    environ = {k: unicode_to_wsgi(v) for k,v in os.environ.items()}
    environ[‘wsgi.input‘]        = sys.stdin.buffer
    environ[‘wsgi.errors‘]       = sys.stderr
    environ[‘wsgi.version‘]      = (1, 0)
    environ[‘wsgi.multithread‘]  = False
    environ[‘wsgi.multiprocess‘] = True
    environ[‘wsgi.run_once‘]     = True
    if environ.get(‘HTTPS‘, ‘off‘) in (‘on‘, ‘1‘):
        environ[‘wsgi.url_scheme‘] = ‘https‘
    else:
        environ[‘wsgi.url_scheme‘] = ‘http‘
    headers_set = []
    headers_sent = []
    # 将应答的数据输出到终端
    def write(data):
        out = sys.stdout.buffer
        if not headers_set:
             raise AssertionError("write() before start_response()")
        elif not headers_sent:
             # Before the first output, send the stored headers
             status, response_headers = headers_sent[:] = headers_set
             out.write(wsgi_to_bytes(‘Status: %s\r\n‘ % status))
             for header in response_headers:
                 out.write(wsgi_to_bytes(‘%s: %s\r\n‘ % header))
             out.write(wsgi_to_bytes(‘\r\n‘))
        out.write(data)
        out.flush()
    # 根据程序传过来的状态和头部参数设置响应的状态和头部
    def start_response(status, response_headers, exc_info=None):
        if exc_info:
            try:
                if headers_sent:
                    # Re-raise original exception if headers sent
                    raise exc_info[1].with_traceback(exc_info[2])
            finally:
                exc_info = None     # avoid dangling circular ref
        elif headers_set:
            raise AssertionError("Headers already set!")
        headers_set[:] = [status, response_headers]
        return write
    # 调用客户端的对象，并且输出返回的结果
    result = application(environ, start_response)
    try:
        for data in result:
            if data:    # don‘t send headers until body appears
                write(data)
        if not headers_sent:
            write(‘‘)   # send headers now if body was empty
    finally:
        if hasattr(result, ‘close‘):
            result.close()

HELLO_WORLD = b"Hello world!\n"
# 1. 可调用对象是一个函数
def application(environ, start_response):
    # HTTP response code and message
    status = ‘200 OK‘
    # 应答的头部是一个列表，每对键值都必须是一个 tuple。
    response_headers = [(‘Content-Type‘, ‘text/plain‘),
                        (‘Content-Length‘, str(len(HELLO_WORLD)))]
    # 调用服务器程序提供的 start_response，填入两个参数
    start_response(status, response_headers)
    # 返回必须是 iterable
    return [HELLO_WORLD]

# 2. 可调用对象是一个类
class AppClass:
    """这里的可调用对象就是 AppClass 这个类，调用它就能生成可以迭代的结果。          使用方法类似于：
        for result in AppClass(env, start_response):
             do_somthing(result)
    """
    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

# 3. 可调用对象是一个实例
class AppClass:
    """这里的可调用对象就是 AppClass 的实例，使用方法类似于：
        app = AppClass()
        for result in app(environ, start_response):
             do_somthing(result)
    """
    def __init__(self):
        pass
    def __call__(self, environ, start_response):
        status = ‘200 OK‘
        response_headers = [(‘Content-type‘, ‘text/plain‘)]
        self.start(status, response_headers)
        yield HELLO_WORLD