Move method increment_filename from FileNotebookManager to NotebookManager

The implementation requires only a minor change (call notebook_exists
rather than checking for file existence) to be universally usable
in other notebook managers.

IPython/html/services/notebooks/filenbmanager.py

@@ -82,16 +82,6 b' class FileNotebookManager(NotebookManager):'
                  for name in names]
         return names
 
-    def increment_filename(self, basename, path='', ext='.ipynb'):
-        """Return a non-used filename of the form basename<int>."""
-        path = path.strip('/')
-        for i in itertools.count():
-            name = u'{basename}{i}{ext}'.format(basename=basename, i=i, ext=ext)
-            os_path = self.get_os_path(name, path)
-            if not os.path.isfile(os_path):
-                break
-        return name
-
     def path_exists(self, path):
         """Does the API-style path (directory) actually exist?
         

IPython/html/services/notebooks/nbmanager.py

@@ -17,6 +17,7 b' Authors:'
 # Imports
 #-----------------------------------------------------------------------------
 
+import itertools
 import os
 
 from IPython.config.configurable import LoggingConfigurable
@@ -126,8 +127,20 b' class NotebookManager(LoggingConfigurable):'
             The name of a notebook without the ``.ipynb`` file extension.
         path : unicode
             The URL path of the notebooks directory
+
+        Returns
+        -------
+        name : unicode
+            A notebook name (with the .ipynb extension) that starts
+            with basename and does not refer to any existing notebook.
         """
-        return basename
+        path = path.strip('/')
+        for i in itertools.count():
+            name = u'{basename}{i}{ext}'.format(basename=basename, i=i,
+                                                ext=self.filename_ext)
+            if not self.notebook_exists(name, path):
+                break
+        return name
 
     def notebook_exists(self, name, path=''):
         """Returns a True if the notebook exists. Else, returns False.