don't require tornado 3 in `--post serve`

tornado.log is new in 3.0

IPython/nbconvert/postprocessors/serve.py

@@ -1,107 +1,111 b''
 """PostProcessor for serving reveal.js HTML slideshows."""
 #-----------------------------------------------------------------------------
 #Copyright (c) 2013, the IPython Development Team.
 #
 #Distributed under the terms of the Modified BSD License.
 #
 #The full license is in the file COPYING.txt, distributed with this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import webbrowser
 
 from tornado import web, ioloop, httpserver
 from tornado.httpclient import AsyncHTTPClient
 
 from IPython.utils.traitlets import Bool, Unicode, Int
 
 from .base import PostProcessorBase
 
 #-----------------------------------------------------------------------------
 # Classes
 #-----------------------------------------------------------------------------
 
 class ProxyHandler(web.RequestHandler):
     """handler the proxies requests from a local prefix to a CDN"""
     @web.asynchronous
     def get(self, prefix, url):
         """proxy a request to a CDN"""
         proxy_url = "/".join([self.settings['cdn'], url])
         client = self.settings['client']
         client.fetch(proxy_url, callback=self.finish_get)
     
     def finish_get(self, response):
         """finish the request"""
         # copy potentially relevant headers
         for header in ["Content-Type", "Cache-Control", "Date", "Last-Modified", "Expires"]:
             if header in response.headers:
                 self.set_header(header, response.headers[header])
         self.finish(response.body)
 
 class ServePostProcessor(PostProcessorBase):
     """Post processor designed to serve files
     
     Proxies reveal.js requests to a CDN if no local reveal.js is present
     """
 
 
     open_in_browser = Bool(True, config=True,
         help="""Should the browser be opened automatically?"""
     )
     reveal_cdn = Unicode("https://cdn.jsdelivr.net/reveal.js/2.4.0", config=True,
         help="""URL for reveal.js CDN."""
     )
     reveal_prefix = Unicode("reveal.js", config=True, help="URL prefix for reveal.js")
     ip = Unicode("127.0.0.1", config=True, help="The IP address to listen on.")
     port = Int(8000, config=True, help="port for the server to listen on.")
 
     def postprocess(self, input):
         """Serve the build directory with a webserver."""
         dirname, filename = os.path.split(input)
         handlers = [
             (r"/(.+)", web.StaticFileHandler, {'path' : dirname}),
             (r"/", web.RedirectHandler, {"url": "/%s" % filename})
         ]
         
         if ('://' in self.reveal_prefix or self.reveal_prefix.startswith("//")):
             # reveal specifically from CDN, nothing to do
             pass
         elif os.path.isdir(os.path.join(dirname, self.reveal_prefix)):
             # reveal prefix exists
             self.log.info("Serving local %s", self.reveal_prefix)
         else:
             self.log.info("Redirecting %s requests to %s", self.reveal_prefix, self.reveal_cdn)
             handlers.insert(0, (r"/(%s)/(.*)" % self.reveal_prefix, ProxyHandler))
         
         app = web.Application(handlers,
             cdn=self.reveal_cdn,
             client=AsyncHTTPClient(),
         )
         # hook up tornado logging to our logger
-        from tornado import log
-        log.app_log = self.log
+        try:
+            from tornado import log
+            log.app_log = self.log
+        except ImportError:
+            # old tornado (<= 3), ignore
+            pass
     
         http_server = httpserver.HTTPServer(app)
         http_server.listen(self.port, address=self.ip)
         url = "http://%s:%i/%s" % (self.ip, self.port, filename)
         print("Serving your slides at %s" % url)
         print("Use Control-C to stop this server")
         if self.open_in_browser:
             webbrowser.open(url, new=2)
         try:
             ioloop.IOLoop.instance().start()
         except KeyboardInterrupt:
             print("\nInterrupted")
 
 def main(path):
     """allow running this module to serve the slides"""
     server = ServePostProcessor()
     server(path)
     
 if __name__ == '__main__':
     import sys
     main(sys.argv[1])