changeset:   105504:a10361dfbf64
user:        Serhiy Storchaka <storchaka@gmail.com>
date:        Wed Dec 07 11:11:12 2016 +0200
files:       Lib/dbm/dumb.py Lib/test/test_dbm_dumb.py Misc/NEWS
description:
Issue #28847: A deprecation warning is now emitted if the index file is missed
and recreated in the 'r' and 'w' modes (will be an error in future Python
releases).


diff -r 2f59be67830c -r a10361dfbf64 Lib/dbm/dumb.py
--- a/Lib/dbm/dumb.py	Wed Dec 07 11:02:18 2016 +0200
+++ b/Lib/dbm/dumb.py	Wed Dec 07 11:11:12 2016 +0200
@@ -68,7 +68,7 @@
 
         # Handle the creation
         self._create(flag)
-        self._update()
+        self._update(flag)
 
     def _create(self, flag):
         if flag == 'n':
@@ -92,12 +92,17 @@
             f.close()
 
     # Read directory file into the in-memory index dict.
-    def _update(self):
+    def _update(self, flag):
         self._index = {}
         try:
             f = _io.open(self._dirfile, 'r', encoding="Latin-1")
         except OSError:
             self._modified = not self._readonly
+            if flag not in ('c', 'n'):
+                import warnings
+                warnings.warn("The index file is missing, the "
+                              "semantics of the 'c' flag will be used.",
+                              DeprecationWarning, stacklevel=4)
         else:
             self._modified = False
             with f:
diff -r 2f59be67830c -r a10361dfbf64 Lib/test/test_dbm_dumb.py
--- a/Lib/test/test_dbm_dumb.py	Wed Dec 07 11:02:18 2016 +0200
+++ b/Lib/test/test_dbm_dumb.py	Wed Dec 07 11:11:12 2016 +0200
@@ -252,6 +252,20 @@
                 f = dumbdbm.open(_fname, value)
             f.close()
 
+    def test_missing_index(self):
+        with dumbdbm.open(_fname, 'n') as f:
+            pass
+        os.unlink(_fname + '.dir')
+        for value in ('r', 'w'):
+            with self.assertWarnsRegex(DeprecationWarning,
+                                       "The index file is missing, the "
+                                       "semantics of the 'c' flag will "
+                                       "be used."):
+                f = dumbdbm.open(_fname, value)
+            f.close()
+            self.assertEqual(os.path.exists(_fname + '.dir'), value == 'w')
+            self.assertFalse(os.path.exists(_fname + '.bak'))
+
     def test_invalid_flag(self):
         for flag in ('x', 'rf', None):
             with self.assertWarnsRegex(DeprecationWarning,
diff -r 2f59be67830c -r a10361dfbf64 Misc/NEWS
--- a/Misc/NEWS	Wed Dec 07 11:02:18 2016 +0200
+++ b/Misc/NEWS	Wed Dec 07 11:11:12 2016 +0200
@@ -166,7 +166,9 @@
 -------
 
 - Issue #28847: dbm.dumb now supports reading read-only files and no longer
-  writes the index file when it is not changed.
+  writes the index file when it is not changed.  A deprecation warning is now
+  emitted if the index file is missed and recreated in the 'r' and 'w' modes
+  (will be an error in future Python releases).
 
 - Issue #27030: Unknown escapes consisting of ``'\'`` and an ASCII letter in
   re.sub() replacement templates regular expressions now are errors.