Merge pull request #5530 from cool-RR/patch-1

Fix exception causes in handlers.py

notebook/base/handlers.py

@@ -452,7 +452,7 @@ class IPythonHandler(AuthenticatedHandler):
                         msg = "Blocking Cross Origin request from {}.".format(referer)
                     else:
                         msg = "Blocking request from unknown origin"
-                    raise web.HTTPError(403, msg)
+                    raise web.HTTPError(403, msg) from e
             else:
                 raise
 
@@ -542,10 +542,10 @@ class IPythonHandler(AuthenticatedHandler):
         body = self.request.body.strip().decode(u'utf-8')
         try:
             model = json.loads(body)
-        except Exception:
+        except Exception as e:
             self.log.debug("Bad JSON: %r", body)
             self.log.error("Couldn't parse JSON", exc_info=True)
-            raise web.HTTPError(400, u'Invalid JSON in body of request')
+            raise web.HTTPError(400, u'Invalid JSON in body of request') from e
         return model
 
     def write_error(self, status_code, **kwargs):