[Python-checkins] cpython (3.1): Fix #11491. When dbm.open was called with a file which already exists and

[brian.curtin]

http://hg.python.org/cpython/rev/f8d603a2a0af
changeset:   68466:f8d603a2a0af
branch:      3.1
parent:      68449:7af5a9298251
user:        briancurtin <brian.curtin at gmail.com>
date:        Mon Mar 14 15:35:35 2011 -0400
summary:
  Fix #11491. When dbm.open was called with a file which already exists and
the "flag" argument is "n", dbm.error was being raised. As documented,
dbm.open(...,flag='n') will now "Always create a new, empty database,
open for reading and writing", regardless of a previous file existing.

files:
  Lib/dbm/__init__.py
  Lib/test/test_dbm.py
  Misc/ACKS
  Misc/NEWS

diff --git a/Lib/dbm/__init__.py b/Lib/dbm/__init__.py
--- a/Lib/dbm/__init__.py
+++ b/Lib/dbm/__init__.py
@@ -68,10 +68,10 @@
         if not _defaultmod:
             raise ImportError("no dbm clone found; tried %s" % _names)
 
-    # guess the type of an existing database
-    result = whichdb(file)
+    # guess the type of an existing database, if not creating a new one
+    result = whichdb(file) if 'n' not in flag else None
     if result is None:
-        # db doesn't exist
+        # db doesn't exist or 'n' flag was specified to create a new db
         if 'c' in flag or 'n' in flag:
             # file doesn't exist and the new flag was used so use default type
             mod = _defaultmod
diff --git a/Lib/test/test_dbm.py b/Lib/test/test_dbm.py
--- a/Lib/test/test_dbm.py
+++ b/Lib/test/test_dbm.py
@@ -70,6 +70,14 @@
         self.read_helper(f)
         f.close()
 
+    def test_anydbm_creation_n_file_exists_with_invalid_contents(self):
+        with open(_fname, "w") as w:
+            pass # create an empty file
+
+        f = dbm.open(_fname, 'n')
+        self.addCleanup(f.close)
+        self.assertEqual(len(f), 0)
+
     def test_anydbm_modification(self):
         self.init_db()
         f = dbm.open(_fname, 'c')
diff --git a/Misc/ACKS b/Misc/ACKS
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -154,6 +154,7 @@
 Benjamin Collar
 Jeffery Collins
 Paul Colomiets
+Denver Coneybeare
 Matt Conway
 David M. Cooke
 Greg Copeland
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -40,6 +40,10 @@
 Library
 -------
 
+- Issue #11491: dbm.error is no longer raised when dbm.open is called with
+  the "n" as the flag argument and the file exists. The behavior matches
+  the documentation and general logic.
+   
 - Issue #11131: Fix sign of zero in decimal.Decimal plus and minus
   operations when the rounding mode is ROUND_FLOOR.
 

-- 
Repository URL: http://hg.python.org/cpython