Issue #28847: dbm.dumb now supports reading read-only files and no longer

writes the index file when it is not changed.

1 files changed, 5 insertions, 2 deletions

diff --git a/Lib/dbm/dumb.py b/Lib/dbm/dumb.py
index e7c6440ee6..2296dbfd54 100644
--- a/Lib/dbm/dumb.py
+++ b/Lib/dbm/dumb.py
@@ -97,8 +97,9 @@ class _Database(collections.MutableMapping):
         try:
             f = _io.open(self._dirfile, 'r', encoding="Latin-1")
         except OSError:
-            pass
+            self._modified = not self._readonly
         else:
+            self._modified = False
             with f:
                 for line in f:
                     line = line.rstrip()
@@ -113,7 +114,7 @@ class _Database(collections.MutableMapping):
         # CAUTION:  It's vital that _commit() succeed, and _commit() can
         # be called from __del__().  Therefore we must never reference a
         # global in this routine.
-        if self._index is None:
+        if self._index is None or not self._modified:
             return  # nothing to do
 
         try:
@@ -197,6 +198,7 @@ class _Database(collections.MutableMapping):
         elif not isinstance(val, (bytes, bytearray)):
             raise TypeError("values must be bytes or strings")
         self._verify_open()
+        self._modified = True
         if key not in self._index:
             self._addkey(key, self._addval(val))
         else:
@@ -229,6 +231,7 @@ class _Database(collections.MutableMapping):
         if isinstance(key, str):
             key = key.encode('utf-8')
         self._verify_open()
+        self._modified = True
         # The blocks used by the associated value are lost.
         del self._index[key]
         # XXX It's unclear why we do a _commit() here (the code always