##在这里详述 WSGI/SrvWSGI.
服务器 或 getway 每次收到 http客户端 发出的请求都会调用一次相应的 应用程序callable .
举例来说, 这里有一个[[#head-42263f1a3a5d0f4d19ac223b3f534410d2aaeb62-2|简单的 CGI getway]], 
以一个接受一个应用程序对象作为参数的函数来实现的. 
值得注意的是这个简单的例子还拥有有限的错误处理功能,
因为未捕捉的异常默认会写到 {{{sys.error}}} 里并被web服务器记录下来.

The server or gateway invokes the application callable once for each
request it receives from an HTTP client, that is directed at the
application.  To illustrate, here is a [[#head-42263f1a3a5d0f4d19ac223b3f534410d2aaeb62-2|simple CGI gateway]], implemented
as a function taking an application object.  Note that this simple 
example has limited error handling, because by default an uncaught 
exception will be dumped to ``sys.stderr`` and logged by the web 
server.

###[#head-747ebe56750a1de964d165b5b4a56e9eeb2f74a4-2 示例]
==== 示例 ====
{{{#!python
import os, sys

def run_with_cgi(application):

    environ = dict(os.environ.items())
    environ['wsgi.input']        = sys.stdin
    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 = []

    def write(data):
        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
             sys.stdout.write('Status: %s\r\n' % status)
             for header in response_headers:
                 sys.stdout.write('%s: %s\r\n' % header)
             sys.stdout.write('\r\n')

        sys.stdout.write(data)
        sys.stdout.flush()

    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[0], exc_info[1], 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

    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()
}}}