Correctly handle case where channel doesn't exist

http_errors.py

@@ -0,0 +1,11 @@
+class Error4xx(Exception):
+    pass
+class Error404(Error4xx):
+    pass
+
+class Error5xx(Exception):
+    pass
+class Error500(Error5xx):
+    pass
+class Error502(Error5xx):
+    pass

server.py

@@ -4,6 +4,7 @@ import gevent.socket
 
 from gevent.pywsgi import WSGIServer
 from youtube.youtube import youtube
+import http_errors
 import urllib
 import socket
 import socks
@@ -114,7 +115,10 @@ def site_dispatch(env, start_response):
             yield error_code('404 Not Found', start_response)
             return
 
-    
+    except http_errors.Error404 as e:
+        start_response('404 Not Found', ())
+        yield str(e).encode('utf-8')
+
     except socket.error as e:
         start_response('502 Bad Gateway', ())
         print(str(e))

youtube/channel.py

@@ -1,6 +1,7 @@
 import base64
 import youtube.common as common
 from youtube.common import default_multi_get, URL_ORIGIN, get_thumbnail_url, video_id
+import http_errors
 import urllib
 import json
 from string import Template
@@ -193,6 +194,11 @@ def channel_videos_html(polymer_json, current_page=1, current_sort=3, number_of_
             for alert in response['alerts']:
                 result += alert['alertRenderer']['text']['simpleText'] + '\n'
             return result
+        elif 'errors' in response['responseContext']:
+            for error in response['responseContext']['errors']['error']:
+                if error['code'] == 'INVALID_VALUE' and error['location'] == 'browse_id':
+                    raise http_errors.Error404('This channel does not exist')
+            raise
         else:
             raise
     channel_url = microformat['urlCanonical'].rstrip('/')