Convert some custom sort comparison functions to equivalent key functions.
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 9ea92d0..b184ed8 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -2016,7 +2016,7 @@
                 self.extract(tarinfo, path)
 
         # Reverse sort directories.
-        directories.sort(lambda a, b: cmp(a.name, b.name))
+        directories.sort(key=lambda a: a.name)
         directories.reverse()
 
         # Set correct owner, mtime and filemode on directories.