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

Author: gmcrocetti

Doc/library/shelve.rst

@@ -18,7 +18,7 @@ lots of shared  sub-objects.  The keys are ordinary strings.
 
 
 .. function:: open(filename, flag='c', protocol=None, writeback=False, *, \
-                   serializer=None, deserializer=None)
+                   mode=0o666, serializer=None, deserializer=None)
 
    Open a persistent dictionary.  The filename specified is the base filename for
    the underlying database.  As a side-effect, an extension may be added to the
@@ -42,6 +42,9 @@ 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 has the same interpretation as the *mode* parameter of :func:`dbm.open`.
+
    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.
@@ -68,6 +71,9 @@ lots of shared  sub-objects.  The keys are ordinary strings.
       Accepts custom *serializer* and *deserializer* functions in place of
       :func:`pickle.dumps` and :func:`pickle.loads`.
 
+   .. versionchanged:: 3.16
+      Accepts *mode* to control file mode, behavior is the same as in :func:`dbm.open`.
+
    .. note::
 
       Do not rely on the shelf being closed automatically; always call
@@ -209,20 +215,23 @@ Restrictions
 
 
 .. class:: DbfilenameShelf(filename, flag='c', protocol=None, \
-                           writeback=False, *, serializer=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.
 
+   .. versionchanged:: 3.16
+      Added the *mode* parameter.
+
 
 .. _shelve-example:
 

Doc/whatsnew/3.16.rst

@@ -151,6 +151,12 @@ mimetypes
   :meth:`mimetypes.MimeTypes.add_type`.
   Undotted extensions now raise a :exc:`ValueError`.
 
+shelve
+------
+
+* Add suport for custom mode in :func:`shelve.open`.
+  (Contributed by Guilherme Crocetti in :gh:`113093`.)
+
 shutil
 ------
 

Lib/shelve.py

@@ -236,9 +236,9 @@ class DbfilenameShelf(Shelf):
     """
 
     def __init__(self, filename, flag='c', protocol=None, writeback=False, *,
-                 serializer=None, deserializer=None):
+                 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):
@@ -249,18 +249,20 @@ def clear(self):
         self.dict.clear()
 
 def open(filename, flag='c', protocol=None, writeback=False, *,
-         serializer=None, deserializer=None):
+         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=mode,
                            serializer=serializer, deserializer=deserializer)

Lib/test/test_shelve.py

@@ -5,6 +5,7 @@
 import pickle
 import os
 
+from unittest import mock
 from test.support import import_helper, os_helper, subTests
 from collections.abc import MutableMapping
 from test.test_dbm import dbm_iterator
@@ -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`.
+Patch by Guilherme Crocetti.