bpo-36345: Update wsgiref example (GH-12562)

Use literalinclude markup to include Tools/scripts/serve.py code.
Tools/scripts/serve.py first argument on the command line is now optional.

Doc/library/wsgiref.rst

@@ -783,33 +783,7 @@ This is a working "Hello World" WSGI application::
        httpd.serve_forever()
 
 
-Example of a small wsgiref-based web server::
-
-   # Takes a path to serve from and an optional port number (defaults to 8000),
-   # then tries to serve files.  Mime types are guessed from the file names, 404
-   # errors are raised if the file is not found.
-   import sys
-   import os
-   import mimetypes
-   from wsgiref import simple_server, util
-
-   def app(environ, respond):
-       fn = os.path.join(path, environ['PATH_INFO'][1:])
-       if '.' not in fn.split(os.path.sep)[-1]:
-           fn = os.path.join(fn, 'index.html')
-       type = mimetypes.guess_type(fn)[0]
-
-       if os.path.exists(fn):
-           respond('200 OK', [('Content-Type', type)])
-           return util.FileWrapper(open(fn, "rb"))
-       else:
-           respond('404 Not Found', [('Content-Type', 'text/plain')])
-           return [b'not found']
-
-    path = sys.argv[1]
-    port = int(sys.argv[2]) if len(sys.argv) > 2 else 8000
-    with simple_server.make_server('', port, app) as httpd:
-        print("Serving {} on port {}, control-C to stop".format(path, port))
-
-        # Serve until process is killed
-        httpd.serve_forever()
+Example of a WSGI application serving the current directory, accept optional
+directory and port number (default: 8000) on the command line:
+
+.. literalinclude:: ../../Tools/scripts/serve.py

Misc/NEWS.d/next/Documentation/2019-03-26-14-58-34.bpo-36345.r2stx3.rst

+Avoid the duplication of code from ``Tools/scripts/serve.py`` in using the
+:rst:dir:`literalinclude` directive for the basic wsgiref-based web server in the
+documentation of :mod:`wsgiref`.  Contributed by Stéphane Wirtel.

Tools/scripts/serve.py

@@ -25,11 +25,12 @@ def app(environ, respond):
         return [b'not found']
 
 if __name__ == '__main__':
-    path = sys.argv[1]
+    path = sys.argv[1] if len(sys.argv) > 1 else os.getcwd()
     port = int(sys.argv[2]) if len(sys.argv) > 2 else 8000
     httpd = simple_server.make_server('', port, app)
     print("Serving {} on port {}, control-C to stop".format(path, port))
     try:
         httpd.serve_forever()
     except KeyboardInterrupt:
-        print("\b\bShutting down.")
+        print("Shutting down.")
+        httpd.server_close()