bpo-34248: Add filename to error raised in {gnu,ndbm}.open() (GH-8590)

Report the filename to the exception when raising {gdbm,dbm.ndbm}.error in
dbm.gnu.open() and dbm.ndbm.open() functions, so it gets printed when the
exception is raised, and can also be obtained by the filename attribute of the
exception object.

Lib/test/test_dbm_gnu.py

@@ -144,6 +144,13 @@ class TestGdbm(unittest.TestCase):
             self.assertTrue(b'key' in db)
             self.assertEqual(db[b'key'], b'value')
 
+    def test_nonexisting_file(self):
+        nonexisting_file = 'nonexisting-file'
+        with self.assertRaises(gdbm.error) as cm:
+            gdbm.open(nonexisting_file)
+        self.assertIn(nonexisting_file, str(cm.exception))
+        self.assertEqual(cm.exception.filename, nonexisting_file)
+
 
 if __name__ == '__main__':
     unittest.main()

Lib/test/test_dbm_ndbm.py

@@ -105,6 +105,12 @@ class DbmTestCase(unittest.TestCase):
             self.assertTrue(b'key' in db)
             self.assertEqual(db[b'key'], b'value')
 
+    def test_nonexisting_file(self):
+        nonexisting_file = 'nonexisting-file'
+        with self.assertRaises(dbm.ndbm.error) as cm:
+            dbm.ndbm.open(nonexisting_file)
+        self.assertIn(nonexisting_file, str(cm.exception))
+        self.assertEqual(cm.exception.filename, nonexisting_file)
 
 
 if __name__ == '__main__':

Misc/NEWS.d/next/Library/2018-07-31-23-00-09.bpo-34248.5U6wwc.rst

+Report filename in the exception raised when the database file cannot be opened
+by :func:`dbm.gnu.open` and :func:`dbm.ndbm.open` due to OS-related error.
+Patch by Zsolt Cserna.

Modules/_dbmmodule.c

@@ -62,7 +62,7 @@ newdbmobject(const char *file, int flags, int mode)
     dp->di_size = -1;
     /* See issue #19296 */
     if ( (dp->di_dbm = dbm_open((char *)file, flags, mode)) == 0 ) {
-        PyErr_SetFromErrno(DbmError);
+        PyErr_SetFromErrnoWithFilename(DbmError, file);
         Py_DECREF(dp);
         return NULL;
     }

Modules/_gdbmmodule.c

@@ -75,7 +75,7 @@ newdbmobject(const char *file, int flags, int mode)
     errno = 0;
     if ((dp->di_dbm = gdbm_open((char *)file, 0, flags, mode, NULL)) == 0) {
         if (errno != 0)
-            PyErr_SetFromErrno(DbmError);
+            PyErr_SetFromErrnoWithFilename(DbmError, file);
         else
             PyErr_SetString(DbmError, gdbm_strerror(gdbm_errno));
         Py_DECREF(dp);