fix os.path.samefile backport on py2 + Windows

os.path.samefile is available everywhere but Windows + py2.
Backporting the py3 implementation doesn't work because
`os.stat` on Windows py2 returns 0 for st_ino and st_dev,
which will always be equal.

In this case, use case-insensitive path comparison, plus full-stat comparison (times included).

notebook/services/contents/filemanager.py

@@ -24,9 +24,14 @@ from . import tz
 from notebook.utils import (
     is_hidden,
     to_api_path,
-    same_file,
 )
 
+try:
+    from os.path import samefile
+except ImportError:
+    # windows + py2
+    from notebook.utils import samefile_simple as samefile
+
 _script_exporter = None
 
 
@@ -123,7 +128,7 @@ class FileContentsManager(FileManagerMixin, ContentsManager):
                 self.log.error("Post-save hook failed o-n %s", os_path, exc_info=True)
                 raise web.HTTPError(500, u'Unexpected error while running post hook save: %s' % e)
 
-    @validate('root_dir') 
+    @validate('root_dir')
     def _validate_root_dir(self, proposal):
         """Do a bit of validation of the root_dir."""
         value = proposal['value']
@@ -469,7 +474,7 @@ class FileContentsManager(FileManagerMixin, ContentsManager):
         old_os_path = self._get_os_path(old_path)
 
         # Should we proceed with the move?
-        if os.path.exists(new_os_path) and not same_file(old_os_path, new_os_path):
+        if os.path.exists(new_os_path) and not samefile(old_os_path, new_os_path):
             raise web.HTTPError(409, u'File already exists: %s' % new_path)
 
         # Move the file

notebook/utils.py

@@ -141,11 +141,16 @@ def is_hidden(abs_path, abs_root=''):
 
     return False
 
-def same_file(path, other_path):
+def samefile_simple(path, other_path):
     """
-    Check if path and other_path are hard links to the same file. This is a
-    utility implementation of Python's os.path.samefile which is not available
-    with Python 2.x and Windows.
+    Fill in for os.path.samefile when it is unavailable (Windows+py2).
+
+    Do a case-insensitive string comparison in this case
+    plus comparing the full stat result (including times)
+    because Windows + py2 doesn't support the stat fields
+    needed for identifying if it's the same file (st_ino, st_dev).
+
+    Only to be used if os.path.samefile is not available.
 
     Parameters
     -----------
@@ -158,12 +163,13 @@ def same_file(path, other_path):
     """
     path_stat = os.stat(path)
     other_path_stat = os.stat(other_path)
-    return (path_stat.st_ino == other_path_stat.st_ino and 
-            path_stat.st_dev == other_path_stat.st_dev)
+    return (path.lower() == other_path.lower()
+        and path_stat == other_path_stat)
+
 
 def to_os_path(path, root=''):
     """Convert an API path to a filesystem path
-    
+
     If given, root will be prepended to the path.
     root must be a filesystem path already.
     """