make FilesRedirectHandler redirect logic accessible

from a static method

instead of calling FRH.get(self), which doesn't work on Python 2
due to unbound method class checking.

IPython/html/base/handlers.py

@@ -464,7 +464,13 b' class TrailingSlashHandler(web.RequestHandler):'
 
 class FilesRedirectHandler(IPythonHandler):
     """Handler for redirecting relative URLs to the /files/ handler"""
-    def get(self, path=''):
+    
+    @staticmethod
+    def redirect_to_files(self, path):
+        """make redirect logic a reusable static method
+        
+        so it can be called from other handlers.
+        """
         cm = self.contents_manager
         if cm.dir_exists(path):
             # it's a *directory*, redirect to /tree
@@ -488,6 +494,9 b' class FilesRedirectHandler(IPythonHandler):'
         url = url_escape(url)
         self.log.debug("Redirecting %s to %s", self.request.path, url)
         self.redirect(url)
+    
+    def get(self, path=''):
+        return self.redirect_to_files(self, path)
 
 
 #-----------------------------------------------------------------------------

IPython/html/notebook/handlers.py

@@ -28,12 +28,12 b' class NotebookHandler(IPythonHandler):'
         except web.HTTPError as e:
             if e.status_code == 404 and 'files' in path.split('/'):
                 # 404, but '/files/' in URL, let FilesRedirect take care of it
-                return FilesRedirectHandler.get(self, path)
+                return FilesRedirectHandler.redirect_to_files(self, path)
             else:
                 raise
         if model['type'] != 'notebook':
             # not a notebook, redirect to files
-            return FilesRedirectHandler.get(self, path)
+            return FilesRedirectHandler.redirect_to_files(self, path)
         name = url_escape(path.rsplit('/', 1)[-1])
         path = url_escape(path)
         self.write(self.render_template('notebook.html',