python · furkanonder · Nov 20, 2022 · Dec 3, 2022 · Dec 3, 2022 · Dec 3, 2022
diff --git a/Doc/library/shelve.rst b/Doc/library/shelve.rst
@@ -17,7 +17,7 @@ This includes most class instances, recursive data types, and objects containing
 lots of shared  sub-objects.  The keys are ordinary strings.
 
 
-.. function:: open(filename, flag='c', protocol=None, writeback=False)
+.. function:: open(filename, flag='c', protocol=None, writeback=False, 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
@@ -41,13 +41,24 @@ lots of shared  sub-objects.  The keys are ordinary strings.
    determine which accessed entries are mutable, nor which ones were actually
    mutated).
 
+   By default, :mod:`shelve` uses :func:`pickle.dumps` and :func:`pickle.loads`
+   for serializing and deserializing. However *serializer* can be the function
+   that takes the :term:`bytes-like object` and returns the object. *deserializer*
+   can be the function that takes the object and returns :class:`bytes`. For example,
+   :keyword:`lambda`, which the :mod:`pickle` does not support, can be used in
+   :mod:`shelve` using the serializer and deserializer functions, which do support
+   the :keyword:`lambda`.
+
    .. versionchanged:: 3.10
       :data:`pickle.DEFAULT_PROTOCOL` is now used as the default pickle
       protocol.
 
    .. versionchanged:: 3.11
       Accepts :term:`path-like object` for filename.
 
+   .. versionchanged:: 3.12
+      Accepts *serializer* and *deserializer*.
+
    .. note::
 
       Do not rely on the shelf being closed automatically; always call

diff --git a/Lib/shelve.py b/Lib/shelve.py
@@ -56,13 +56,18 @@
 the persistent dictionary on disk, if feasible).
 """
 
-from pickle import DEFAULT_PROTOCOL, Pickler, Unpickler
+from pickle import DEFAULT_PROTOCOL, Unpickler, dumps, loads
 from io import BytesIO
 
 import collections.abc
 
 __all__ = ["Shelf", "BsdDbShelf", "DbfilenameShelf", "open"]
 
+
+class ShelveError(Exception):
+    pass
+
+
 class _ClosedDict(collections.abc.MutableMapping):
     'Marker for a closed dict.  Access attempts raise a ValueError.'
 
@@ -82,7 +87,7 @@ class Shelf(collections.abc.MutableMapping):
     """
 
     def __init__(self, dict, protocol=None, writeback=False,
-                 keyencoding="utf-8"):
+                 keyencoding="utf-8", *, serializer=None, deserializer=None):
         self.dict = dict
         if protocol is None:
             protocol = DEFAULT_PROTOCOL
@@ -91,6 +96,15 @@ def __init__(self, dict, protocol=None, writeback=False,
         self.cache = {}
         self.keyencoding = keyencoding
 
+        if serializer is None and deserializer is None:
+            self.serializer = dumps
+            self.deserializer = loads
+        elif (serializer is None) ^ (deserializer is None):
+            raise ShelveError("Serializer and deserializer must be defined together.")
+        else:
+            self.serializer = serializer
+            self.deserializer = deserializer
+
     def __iter__(self):
         for k in self.dict.keys():
             yield k.decode(self.keyencoding)
@@ -110,19 +124,16 @@ def __getitem__(self, key):
         try:
             value = self.cache[key]
         except KeyError:
-            f = BytesIO(self.dict[key.encode(self.keyencoding)])
-            value = Unpickler(f).load()
+            f = self.dict[key.encode(self.keyencoding)]
+            value = self.deserializer(f)
             if self.writeback:
                 self.cache[key] = value
         return value
 
     def __setitem__(self, key, value):
         if self.writeback:
             self.cache[key] = value
-        f = BytesIO()
-        p = Pickler(f, self._protocol)
-        p.dump(value)
-        self.dict[key.encode(self.keyencoding)] = f.getvalue()
+        self.dict[key.encode(self.keyencoding)] = self.serializer(value, self._protocol)
 
     def __delitem__(self, key):
         del self.dict[key.encode(self.keyencoding)]
@@ -222,12 +233,12 @@ 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):
+    def __init__(self, filename, flag='c', protocol=None, writeback=False, *, serializer=None, deserializer=None):
         import dbm
-        Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback)
+        Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback, serializer=serializer, deserializer=deserializer)
 
 
-def open(filename, flag='c', protocol=None, writeback=False):
+def open(filename, flag='c', protocol=None, writeback=False, *, serializer=None, deserializer=None):
     """Open a persistent dictionary for reading and writing.
 
     The filename parameter is the base filename for the underlying
@@ -240,4 +251,4 @@ def open(filename, flag='c', protocol=None, writeback=False):
     See the module's __doc__ string for an overview of the interface.
     """
 
-    return DbfilenameShelf(filename, flag, protocol, writeback)
+    return DbfilenameShelf(filename, flag, protocol, writeback, serializer, deserializer)
diff --git a/Lib/test/test_shelve.py b/Lib/test/test_shelve.py
@@ -3,6 +3,8 @@
 import shelve
 import pickle
 import os
+from io import BytesIO
+from pydoc import locate
 
 from test.support import os_helper
 from collections.abc import MutableMapping
@@ -165,6 +167,58 @@ def test_default_protocol(self):
         with shelve.Shelf({}) as s:
             self.assertEqual(s._protocol, pickle.DEFAULT_PROTOCOL)
 
+    def test_custom_serializer_and_deserializer(self):
+        def serializer(obj, protocol=None):
+            return bytes(f"{type(obj).__name__}", 'utf-8')
+
+        def deserializer(data):
+            value = BytesIO(data).read()
+            return locate(value.decode("utf-8"))
+
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
+
+        with shelve.open(self.fn, serializer=serializer, deserializer=deserializer) as s:
+            num = 1
+            s['number'] = num
+            self.assertEqual(s['number'], type(num))
+
+        with self.assertRaises(AssertionError):
+            def serializer(obj, protocol=None):
+                return bytes(f"{type(obj).__name__}", 'utf-8')
+
+            def deserializer(data):
+                pass
+
+            with shelve.open(self.fn, serializer=serializer, deserializer=deserializer) as s:
+                s['number'] = 100
+                self.assertEqual(s['number'], 100)
+
+        with self.assertRaises(TypeError):
+            def serializer(obj, protocol=None):
+                pass
+
+            def deserializer(data):
+                return BytesIO(data).read().decode("utf-8")
+
+            with shelve.open(self.fn, serializer=serializer, deserializer=deserializer) as s:
+                s['number'] = 100
+                self.assertEqual(s['number'], 100)
+
+    def test_missing_custom_deserializer(self):
+        def serializer(obj, protocol=None):
+            pass
+
+        with self.assertRaises(shelve.ShelveError):
+            shelve.Shelf({}, protocol=2, writeback=False, serializer=serializer)
+
+    def test_missing_custom_serializer(self):
+        def deserializer(data):
+            pass
+
+        with self.assertRaises(shelve.ShelveError):
+            shelve.Shelf({}, protocol=2, writeback=False, deserializer=deserializer)
+
 
 class TestShelveBase:
     type2test = shelve.Shelf

diff --git a/Misc/NEWS.d/next/Documentation/2022-12-05-19-21-22.gh-issue-99631.WVkNJl.rst b/Misc/NEWS.d/next/Documentation/2022-12-05-19-21-22.gh-issue-99631.WVkNJl.rst
@@ -0,0 +1 @@
+Shelve module accepts serializer and deserializer functions.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Shelve module accepts serializer and deserializer functions.