bpo-33106: change dbm key deletion error for readonly file from KeyError to dbm.error (#6295)

Author: zhangyangyu

Doc/library/dbm.rst

@@ -73,6 +73,10 @@ available, as well as :meth:`get` and :meth:`setdefault`.
 .. versionchanged:: 3.2
  :meth:`get` and :meth:`setdefault` are now available in all database modules.
 
+.. versionchanged:: 3.8
+ Deleting a key from a read-only database raises database module specific error
+ instead of :exc:`KeyError`.
+
 Key and values are always stored as bytes. This means that when
 strings are used they are implicitly converted to the default encoding before
 being stored.

Doc/whatsnew/3.8.rst

@@ -483,6 +483,12 @@ Changes in the Python API
  external entities by default.
  (Contributed by Christian Heimes in :issue:`17239`.)
 
+* Deleting a key from a read-only :mod:`dbm` database (:mod:`dbm.dumb`,
+ :mod:`dbm.gnu` or :mod:`dbm.ndbm`) raises :attr:`error` (:exc:`dbm.dumb.error`,
+ :exc:`dbm.gnu.error` or :exc:`dbm.ndbm.error`) instead of :exc:`KeyError`.
+ (Contributed by Xiang Zhang in :issue:`33106`.)
+
+
 CPython bytecode changes
 ------------------------
 

Lib/dbm/dumb.py

@@ -185,7 +185,7 @@ def _addkey(self, key, pos_and_siz_pair):
 
  def __setitem__(self, key, val):
  if self._readonly:
- raise ValueError('The database is opened for reading only')
+ raise error('The database is opened for reading only')
  if isinstance(key, str):
  key = key.encode('utf-8')
  elif not isinstance(key, (bytes, bytearray)):
@@ -222,7 +222,7 @@ def __setitem__(self, key, val):
 
  def __delitem__(self, key):
  if self._readonly:
- raise ValueError('The database is opened for reading only')
+ raise error('The database is opened for reading only')
  if isinstance(key, str):
  key = key.encode('utf-8')
  self._verify_open()

Lib/test/test_dbm_dumb.py

@@ -82,10 +82,10 @@ def test_dumbdbm_read(self):
  self.init_db()
  f = dumbdbm.open(_fname, 'r')
  self.read_helper(f)
- with self.assertRaisesRegex(ValueError,
+ with self.assertRaisesRegex(dumbdbm.error,
  'The database is opened for reading only'):
  f[b'g'] = b'x'
- with self.assertRaisesRegex(ValueError,
+ with self.assertRaisesRegex(dumbdbm.error,
  'The database is opened for reading only'):
  del f[b'a']
  # get() works as in the dict interface

Lib/test/test_dbm_gnu.py

@@ -131,6 +131,17 @@ def test_unicode(self):
  self.assertEqual(db['Unicode key \U0001f40d'],
  'Unicode value \U0001f40d'.encode())
 
+ def test_write_readonly_file(self):
+ with gdbm.open(filename, 'c') as db:
+ db[b'bytes key'] = b'bytes value'
+ with gdbm.open(filename, 'r') as db:
+ with self.assertRaises(gdbm.error):
+ del db[b'not exist key']
+ with self.assertRaises(gdbm.error):
+ del db[b'bytes key']
+ with self.assertRaises(gdbm.error):
+ db[b'not exist key'] = b'not exist value'
+
  @unittest.skipUnless(TESTFN_NONASCII,
  'requires OS support of non-ASCII encodings')
  def test_nonascii_filename(self):

Lib/test/test_dbm_ndbm.py

@@ -90,6 +90,17 @@ def test_unicode(self):
  self.assertEqual(db['Unicode key \U0001f40d'],
  'Unicode value \U0001f40d'.encode())
 
+ def test_write_readonly_file(self):
+ with dbm.ndbm.open(self.filename, 'c') as db:
+ db[b'bytes key'] = b'bytes value'
+ with dbm.ndbm.open(self.filename, 'r') as db:
+ with self.assertRaises(error):
+ del db[b'not exist key']
+ with self.assertRaises(error):
+ del db[b'bytes key']
+ with self.assertRaises(error):
+ db[b'not exist key'] = b'not exist value'
+
  @unittest.skipUnless(support.TESTFN_NONASCII,
  'requires OS support of non-ASCII encodings')
  def test_nonascii_filename(self):

Misc/NEWS.d/next/Library/2018-03-30-01-20-35.bpo-33106.zncfvW.rst

@@ -0,0 +1,2 @@
+Deleting a key from a read-only dbm database raises module specfic error
+instead of KeyError.

Modules/_dbmmodule.c

@@ -36,6 +36,7 @@ class _dbm.dbm "dbmobject *" "&Dbmtype"
 
 typedef struct {
  PyObject_HEAD
+ int flags;
  int di_size; /* -1 means recompute */
  DBM *di_dbm;
 } dbmobject;
@@ -60,6 +61,7 @@ newdbmobject(const char *file, int flags, int mode)
  if (dp == NULL)
  return NULL;
  dp->di_size = -1;
+ dp->flags = flags;
  /* See issue #19296 */
  if ( (dp->di_dbm = dbm_open((char *)file, flags, mode)) == 0 ) {
  PyErr_SetFromErrnoWithFilename(DbmError, file);
@@ -143,13 +145,20 @@ dbm_ass_sub(dbmobject *dp, PyObject *v, PyObject *w)
  if (w == NULL) {
  if ( dbm_delete(dp->di_dbm, krec) < 0 ) {
  dbm_clearerr(dp->di_dbm);
- PyErr_SetObject(PyExc_KeyError, v);
+ /* we might get a failure for reasons like file corrupted,
+ but we are not able to distinguish it */
+ if (dp->flags & O_RDWR) {
+ PyErr_SetObject(PyExc_KeyError, v);
+ }
+ else {
+ PyErr_SetString(DbmError, "cannot delete item from database");
+ }
  return -1;
  }
  } else {
  if ( !PyArg_Parse(w, "s#", &drec.dptr, &tmp_size) ) {
  PyErr_SetString(PyExc_TypeError,
- "dbm mappings have byte or string elements only");
+ "dbm mappings have bytes or string elements only");
  return -1;
  }
  drec.dsize = tmp_size;
@@ -335,7 +344,7 @@ _dbm_dbm_setdefault_impl(dbmobject *self, const char *key,
  else {
  if ( !PyArg_Parse(default_value, "s#", &val.dptr, &tmp_size) ) {
  PyErr_SetString(PyExc_TypeError,
- "dbm mappings have byte string elements only");
+ "dbm mappings have bytes or string elements only");
  return NULL;
  }
  val.dsize = tmp_size;

Modules/_gdbmmodule.c

@@ -186,14 +186,19 @@ dbm_ass_sub(dbmobject *dp, PyObject *v, PyObject *w)
  dp->di_size = -1;
  if (w == NULL) {
  if (gdbm_delete(dp->di_dbm, krec) < 0) {
- PyErr_SetObject(PyExc_KeyError, v);
+ if (gdbm_errno == GDBM_ITEM_NOT_FOUND) {
+ PyErr_SetObject(PyExc_KeyError, v);
+ }
+ else {
+ PyErr_SetString(DbmError, gdbm_strerror(gdbm_errno));
+ }
  return -1;
  }
  }
  else {
  if (!PyArg_Parse(w, "s#", &drec.dptr, &drec.dsize)) {
  PyErr_SetString(PyExc_TypeError,
- "gdbm mappings have byte or string elements only");
+ "gdbm mappings have bytes or string elements only");
  return -1;
  }
  errno = 0;