changed default filename for a copied notebook (#4618)

notebook/services/contents/manager.py

@@ -331,7 +331,10 @@ class ContentsManager(LoggingConfigurable):
         """
         # Extract the full suffix from the filename (e.g. .tar.gz)
         path = path.strip('/')
-        basename, dot, ext = filename.partition('.')
+        basename, dot, ext = filename.rpartition('.')
+        if ext != 'ipynb':
+                basename, dot, ext = filename.partition('.')
+                
         suffix = dot + ext
 
         for i in itertools.count():
@@ -425,6 +428,8 @@ class ContentsManager(LoggingConfigurable):
 
         If to_path not specified, it will be the parent directory of from_path.
         If to_path is a directory, filename will increment `from_path-Copy#.ext`.
+        Considering multi-part extensions, the Copy# part will be placed before the first dot for all the extensions except `ipynb`.
+        For easier manual searching in case of notebooks, the Copy# part will be placed before the last dot. 
 
         from_path must be a full path to a file.
         """