diff -r 6e26b5291c41 Lib/pydoc.py
--- a/Lib/pydoc.py	Wed Nov 19 00:11:05 2014 +0200
+++ b/Lib/pydoc.py	Wed Nov 19 09:24:38 2014 +0200
@@ -2098,7 +2098,6 @@ pydoc</strong> by Ka-Ping Yee &lt;ping@l
         def __init__(self, port, callback):
             host = 'localhost'
             self.address = (host, port)
-            self.url = 'http://%s:%d/' % (host, port)
             self.callback = callback
             self.base.__init__(self, self.address, self.handler)
 
@@ -2111,6 +2110,7 @@ pydoc</strong> by Ka-Ping Yee &lt;ping@l
 
         def server_activate(self):
             self.base.server_activate(self)
+            self.url = 'http://%s:%d/' % (self.address[0], self.server_port)
             if self.callback: self.callback(self)
 
     DocServer.base = BaseHTTPServer.HTTPServer
@@ -2384,7 +2384,8 @@ def cli():
     Search for a keyword in the synopsis lines of all available modules.
 
 %s -p <port>
-    Start an HTTP server on the given port on the local machine.
+    Start an HTTP server on the given port on the local machine.  Port
+    number 0 can be used to get an arbitrary unused port.
 
 %s -g
     Pop up a graphical interface for finding and serving documentation.