gh-113093: add parameter 'mode' in shelve.open, letting users control file's type and access permissions

Author: gmcrocetti

Doc/library/shelve.rst

@@ -42,6 +42,11 @@ lots of shared  sub-objects.  The keys are ordinary strings.
    determine which accessed entries are mutable, nor which ones were actually
    mutated).
 
+   The optional *mode* parameter controls the file mode (permissions) when creating
+   a new shelf. It is passed to :func:`dbm.open` and defaults to ``0o666`` (octal),
+   which means read and write permissions for everyone, subject to the current umask.
+   This parameter has no effect if the database already exists.
+
    By default, :mod:`!shelve` uses :func:`pickle.dumps` and :func:`pickle.loads`
    for serializing and deserializing. This can be changed by supplying
    *serializer* and *deserializer*, respectively.
@@ -209,19 +214,19 @@ Restrictions
 
 
 .. class:: DbfilenameShelf(filename, flag='c', protocol=None, \
-                           writeback=False, *, serializer=None, \
-                           deserializer=None)
+                           writeback=False, mode=0o666, *, \
+                           serializer=None, deserializer=None)
 
    A subclass of :class:`Shelf` which accepts a *filename* instead of a dict-like
    object.  The underlying file will be opened using :func:`dbm.open`.  By
    default, the file will be created and opened for both read and write.  The
    optional *flag* parameter has the same interpretation as for the
-   :func:`.open` function.  The optional *protocol*, *writeback*, *serializer*
+   :func:`.open` function.  The optional *mode*, *protocol*, *writeback*, *serializer*
    and *deserializer* parameters have the same interpretation as in
    :func:`~shelve.open`.
 
    .. versionchanged:: 3.15
-      Added the *serializer* and *deserializer* parameters.
+      Added the *mode*, *serializer* and *deserializer* parameters.
 
 
 .. _shelve-example:
@@ -284,4 +289,3 @@ Exceptions
 
    Module :mod:`pickle`
       Object serialization used by :mod:`!shelve`.
-

Doc/whatsnew/3.15.rst

@@ -1024,7 +1024,8 @@ shelve
 * Add support for custom serialization and deserialization functions
   in the :mod:`shelve` module.
   (Contributed by Furkan Onder in :gh:`99631`.)
-
+* Add suport for custom mode in :func:`shelve.open`.
+  (Contributed by Guilherme Crocetti in :gh:`113093`.)
 
 socket
 ------

Lib/shelve.py

@@ -235,10 +235,10 @@ class DbfilenameShelf(Shelf):
     See the module's __doc__ string for an overview of the interface.
     """
 
-    def __init__(self, filename, flag='c', protocol=None, writeback=False, *,
-                 serializer=None, deserializer=None):
+    def __init__(self, filename, flag='c', protocol=None, writeback=False,
+                 mode=0o666, *, serializer=None, deserializer=None):
         import dbm
-        Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback,
+        Shelf.__init__(self, dbm.open(filename, flag, mode), protocol, writeback,
                        serializer=serializer, deserializer=deserializer)
 
     def clear(self):
@@ -248,19 +248,21 @@ def clear(self):
         self.cache.clear()
         self.dict.clear()
 
-def open(filename, flag='c', protocol=None, writeback=False, *,
-         serializer=None, deserializer=None):
+def open(filename, flag='c', protocol=None, writeback=False,
+         mode=0o666, *, serializer=None, deserializer=None):
     """Open a persistent dictionary for reading and writing.
 
     The filename parameter is the base filename for the underlying
     database.  As a side-effect, an extension may be added to the
     filename and more than one file may be created.  The optional flag
     parameter has the same interpretation as the flag parameter of
     dbm.open(). The optional protocol parameter specifies the
-    version of the pickle protocol.
+    version of the pickle protocol. The optional mode parameter is
+    passed to dbm.open() and controls the file mode when creating a
+    new shelf, set to 0666 by default.
 
     See the module's __doc__ string for an overview of the interface.
     """
 
-    return DbfilenameShelf(filename, flag, protocol, writeback,
+    return DbfilenameShelf(filename, flag, protocol, writeback, mode,
                            serializer=serializer, deserializer=deserializer)

Lib/test/test_shelve.py

@@ -1,5 +1,6 @@
 import array
 import unittest
+from unittest import mock
 import dbm
 import shelve
 import pickle
@@ -47,6 +48,12 @@ class TestCase(unittest.TestCase):
     dirname = os_helper.TESTFN
     fn = os.path.join(os_helper.TESTFN, "shelftemp.db")
 
+    @mock.patch("dbm.open", autospec=True)
+    def test_open_calls_dbm_as_expected(self, dbm_open):
+        shelf_open_mode = 0o433
+        shelve.open(filename=self.fn, mode=shelf_open_mode)
+        dbm_open.assert_called_once_with(self.fn, 'c', shelf_open_mode)
+
     def test_close(self):
         d1 = {}
         s = shelve.Shelf(d1, protocol=2, writeback=False)

Misc/NEWS.d/next/Library/2026-04-17-10-42-00.gh-issue-113093.KzsNvW.rst

@@ -0,0 +1,2 @@
+Add parameter *mode* in :func:`shelve.open`.
+Contributed by Guilherme Crocetti.