Backport NamedTuple and TypedDict deprecations from Python 3.13 (#240)

Author: JelleZijlstra

CHANGELOG.md

@@ -30,6 +30,15 @@
 - Allow classes to inherit from both `typing.Protocol` and `typing_extensions.Protocol`
   simultaneously. Since v4.6.0, this caused `TypeError` to be raised due to a
   metaclass conflict. Patch by Alex Waygood.
+- Backport several deprecations from CPython relating to unusual ways to
+  create `TypedDict`s and `NamedTuple`s. CPython PRs #105609 and #105780
+  by Alex Waygood; `typing_extensions` backport by Jelle Zijlstra.
+  - Creating a `NamedTuple` using the functional syntax with keyword arguments
+    (`NT = NamedTuple("NT", a=int)`) is now deprecated.
+  - Creating a `NamedTuple` with zero fields using the syntax `NT = NamedTuple("NT")`
+    or `NT = NamedTuple("NT", None)` is now deprecated.
+  - Creating a `TypedDict` with zero fields using the syntax `TD = TypedDict("TD")`
+    or `TD = TypedDict("TD", None)` is now deprecated.
 
 # Release 4.6.3 (June 1, 2023)
 

doc/index.rst

@@ -216,6 +216,22 @@ Special typing primitives
 
       Support for the ``__orig_bases__`` attribute was added.
 
+   .. versionchanged:: 4.7.0
+
+      The undocumented keyword argument syntax for creating NamedTuple classes
+      (``NT = NamedTuple("NT", x=int)``) is deprecated, and will be disallowed
+      in Python 3.15. Use the class-based syntax or the functional syntax instead.
+
+   .. versionchanged:: 4.7.0
+
+      When using the functional syntax to create a NamedTuple class, failing to
+      pass a value to the 'fields' parameter (``NT = NamedTuple("NT")``) is
+      deprecated. Passing ``None`` to the 'fields' parameter
+      (``NT = NamedTuple("NT", None)``) is also deprecated. Both will be
+      disallowed in Python 3.15. To create a NamedTuple class with zero fields,
+      use ``class NT(NamedTuple): pass`` or ``NT = NamedTuple("NT", [])``.
+
+
 .. data:: Never
 
    See :py:data:`typing.Never`. In ``typing`` since 3.11.
@@ -355,6 +371,15 @@ Special typing primitives
       This brings ``typing_extensions.TypedDict`` closer to the implementation
       of :py:mod:`typing.TypedDict` on Python 3.9 and higher.
 
+   .. versionchanged:: 4.7.0
+
+      When using the functional syntax to create a TypedDict class, failing to
+      pass a value to the 'fields' parameter (``TD = TypedDict("TD")``) is
+      deprecated. Passing ``None`` to the 'fields' parameter
+      (``TD = TypedDict("TD", None)``) is also deprecated. Both will be
+      disallowed in Python 3.15. To create a TypedDict class with 0 fields,
+      use ``class TD(TypedDict): pass`` or ``TD = TypedDict("TD", {})``.
+
 .. class:: TypeVar(name, *constraints, bound=None, covariant=False,
                    contravariant=False, infer_variance=False, default=...)
 

src/test_typing_extensions.py

@@ -3265,7 +3265,7 @@ def test_typeddict_create_errors(self):
 
     def test_typeddict_errors(self):
         Emp = TypedDict('Emp', {'name': str, 'id': int})
-        if sys.version_info >= (3, 12):
+        if sys.version_info >= (3, 13):
             self.assertEqual(TypedDict.__module__, 'typing')
         else:
             self.assertEqual(TypedDict.__module__, 'typing_extensions')
@@ -3754,6 +3754,45 @@ class MultipleGenericBases(GenericParent[int], GenericParent[float]):
         self.assertEqual(MultipleGenericBases.__orig_bases__, (GenericParent[int], GenericParent[float]))
         self.assertEqual(CallTypedDict.__orig_bases__, (TypedDict,))
 
+    def test_zero_fields_typeddicts(self):
+        T1 = TypedDict("T1", {})
+        class T2(TypedDict): pass
+        try:
+            ns = {"TypedDict": TypedDict}
+            exec("class T3[tvar](TypedDict): pass", ns)
+            T3 = ns["T3"]
+        except SyntaxError:
+            class T3(TypedDict): pass
+        S = TypeVar("S")
+        class T4(TypedDict, Generic[S]): pass
+
+        expected_warning = re.escape(
+            "Failing to pass a value for the 'fields' parameter is deprecated "
+            "and will be disallowed in Python 3.15. "
+            "To create a TypedDict class with 0 fields "
+            "using the functional syntax, "
+            "pass an empty dictionary, e.g. `T5 = TypedDict('T5', {})`."
+        )
+        with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
+            T5 = TypedDict('T5')
+
+        expected_warning = re.escape(
+            "Passing `None` as the 'fields' parameter is deprecated "
+            "and will be disallowed in Python 3.15. "
+            "To create a TypedDict class with 0 fields "
+            "using the functional syntax, "
+            "pass an empty dictionary, e.g. `T6 = TypedDict('T6', {})`."
+        )
+        with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
+            T6 = TypedDict('T6', None)
+
+        for klass in T1, T2, T3, T4, T5, T6:
+            with self.subTest(klass=klass.__name__):
+                self.assertEqual(klass.__annotations__, {})
+                self.assertEqual(klass.__required_keys__, set())
+                self.assertEqual(klass.__optional_keys__, set())
+                self.assertIsInstance(klass(), dict)
+
 
 class AnnotatedTests(BaseTestCase):
 
@@ -4903,8 +4942,10 @@ def test_typing_extensions_defers_when_possible(self):
             exclude |= {
                 'Protocol', 'SupportsAbs', 'SupportsBytes',
                 'SupportsComplex', 'SupportsFloat', 'SupportsIndex', 'SupportsInt',
-                'SupportsRound', 'TypedDict', 'is_typeddict', 'NamedTuple', 'Unpack',
+                'SupportsRound', 'Unpack',
             }
+        if sys.version_info < (3, 13):
+            exclude |= {'NamedTuple', 'TypedDict', 'is_typeddict'}
         for item in typing_extensions.__all__:
             if item not in exclude and hasattr(typing, item):
                 self.assertIs(
@@ -5124,21 +5165,47 @@ class Group(NamedTuple):
                 self.assertFalse(hasattr(Group, attr))
 
     def test_namedtuple_keyword_usage(self):
-        LocalEmployee = NamedTuple("LocalEmployee", name=str, age=int)
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            "Creating NamedTuple classes using keyword arguments is deprecated"
+        ):
+            LocalEmployee = NamedTuple("LocalEmployee", name=str, age=int)
+
         nick = LocalEmployee('Nick', 25)
         self.assertIsInstance(nick, tuple)
         self.assertEqual(nick.name, 'Nick')
         self.assertEqual(LocalEmployee.__name__, 'LocalEmployee')
         self.assertEqual(LocalEmployee._fields, ('name', 'age'))
         self.assertEqual(LocalEmployee.__annotations__, dict(name=str, age=int))
+
         with self.assertRaisesRegex(
             TypeError,
-            'Either list of fields or keywords can be provided to NamedTuple, not both'
+            "Either list of fields or keywords can be provided to NamedTuple, not both"
         ):
             NamedTuple('Name', [('x', int)], y=str)
 
+        with self.assertRaisesRegex(
+            TypeError,
+            "Either list of fields or keywords can be provided to NamedTuple, not both"
+        ):
+            NamedTuple('Name', [], y=str)
+
+        with self.assertRaisesRegex(
+            TypeError,
+            (
+                r"Cannot pass `None` as the 'fields' parameter "
+                r"and also specify fields using keyword arguments"
+            )
+        ):
+            NamedTuple('Name', None, x=int)
+
     def test_namedtuple_special_keyword_names(self):
-        NT = NamedTuple("NT", cls=type, self=object, typename=str, fields=list)
+        with self.assertWarnsRegex(
+            DeprecationWarning,
+            "Creating NamedTuple classes using keyword arguments is deprecated"
+        ):
+            NT = NamedTuple("NT", cls=type, self=object, typename=str, fields=list)
+
         self.assertEqual(NT.__name__, 'NT')
         self.assertEqual(NT._fields, ('cls', 'self', 'typename', 'fields'))
         a = NT(cls=str, self=42, typename='foo', fields=[('bar', tuple)])
@@ -5148,12 +5215,32 @@ def test_namedtuple_special_keyword_names(self):
         self.assertEqual(a.fields, [('bar', tuple)])
 
     def test_empty_namedtuple(self):
-        NT = NamedTuple('NT')
+        expected_warning = re.escape(
+            "Failing to pass a value for the 'fields' parameter is deprecated "
+            "and will be disallowed in Python 3.15. "
+            "To create a NamedTuple class with 0 fields "
+            "using the functional syntax, "
+            "pass an empty list, e.g. `NT1 = NamedTuple('NT1', [])`."
+        )
+        with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
+            NT1 = NamedTuple('NT1')
+
+        expected_warning = re.escape(
+            "Passing `None` as the 'fields' parameter is deprecated "
+            "and will be disallowed in Python 3.15. "
+            "To create a NamedTuple class with 0 fields "
+            "using the functional syntax, "
+            "pass an empty list, e.g. `NT2 = NamedTuple('NT2', [])`."
+        )
+        with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
+            NT2 = NamedTuple('NT2', None)
+
+        NT3 = NamedTuple('NT2', [])
 
         class CNT(NamedTuple):
             pass  # empty body
 
-        for struct in [NT, CNT]:
+        for struct in NT1, NT2, NT3, CNT:
             with self.subTest(struct=struct):
                 self.assertEqual(struct._fields, ())
                 self.assertEqual(struct.__annotations__, {})
@@ -5196,7 +5283,6 @@ def test_copy_and_pickle(self):
                 self.assertIsInstance(jane2, cls)
 
     def test_docstring(self):
-        self.assertEqual(NamedTuple.__doc__, typing.NamedTuple.__doc__)
         self.assertIsInstance(NamedTuple.__doc__, str)
 
     @skipUnless(TYPING_3_8_0, "NamedTuple had a bad signature on <=3.7")

src/typing_extensions.py

@@ -972,7 +972,7 @@ def __round__(self, ndigits: int = 0) -> T_co:
             pass
 
 
-if sys.version_info >= (3, 12):
+if sys.version_info >= (3, 13):
     # The standard library TypedDict in Python 3.8 does not store runtime information
     # about which (if any) keys are optional.  See https://bugs.python.org/issue38834
     # The standard library TypedDict in Python 3.9.0/1 does not honour the "total"
@@ -982,6 +982,7 @@ def __round__(self, ndigits: int = 0) -> T_co:
     # Generic TypedDicts are also impossible using typing.TypedDict on Python <3.11.
     # Aaaand on 3.12 we add __orig_bases__ to TypedDict
     # to enable better runtime introspection.
+    # On 3.13 we deprecate some odd ways of creating TypedDicts.
     TypedDict = typing.TypedDict
     _TypedDictMeta = typing._TypedDictMeta
     is_typeddict = typing.is_typeddict
@@ -1077,13 +1078,14 @@ def __subclasscheck__(cls, other):
 
         __instancecheck__ = __subclasscheck__
 
-    def TypedDict(__typename, __fields=None, *, total=True, **kwargs):
+    def TypedDict(__typename, __fields=_marker, *, total=True, **kwargs):
         """A simple typed namespace. At runtime it is equivalent to a plain dict.
 
-        TypedDict creates a dictionary type that expects all of its
+        TypedDict creates a dictionary type such that a type checker will expect all
         instances to have a certain set of keys, where each key is
         associated with a value of a consistent type. This expectation
-        is not checked at runtime but is only enforced by type checkers.
+        is not checked at runtime.
+
         Usage::
 
             class Point2D(TypedDict):
@@ -1103,19 +1105,39 @@ class Point2D(TypedDict):
             Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
 
         By default, all keys must be present in a TypedDict. It is possible
-        to override this by specifying totality.
-        Usage::
+        to override this by specifying totality::
 
-            class point2D(TypedDict, total=False):
+            class Point2D(TypedDict, total=False):
                 x: int
                 y: int
 
-        This means that a point2D TypedDict can have any of the keys omitted. A type
+        This means that a Point2D TypedDict can have any of the keys omitted. A type
         checker is only expected to support a literal False or True as the value of
         the total argument. True is the default, and makes all items defined in the
         class body be required.
+
+        The Required and NotRequired special forms can also be used to mark
+        individual keys as being required or not required::
+
+            class Point2D(TypedDict):
+                x: int  # the "x" key must always be present (Required is the default)
+                y: NotRequired[int]  # the "y" key can be omitted
+
+        See PEP 655 for more details on Required and NotRequired.
         """
-        if __fields is None:
+        if __fields is _marker or __fields is None:
+            if __fields is _marker:
+                deprecated_thing = "Failing to pass a value for the 'fields' parameter"
+            else:
+                deprecated_thing = "Passing `None` as the 'fields' parameter"
+
+            example = f"`{__typename} = TypedDict({__typename!r}, {{}})`"
+            deprecation_msg = (
+                f"{deprecated_thing} is deprecated and will be disallowed in "
+                "Python 3.15. To create a TypedDict class with 0 fields "
+                "using the functional syntax, pass an empty dictionary, e.g. "
+            ) + example + "."
+            warnings.warn(deprecation_msg, DeprecationWarning, stacklevel=2)
             __fields = kwargs
         elif kwargs:
             raise TypeError("TypedDict takes either a dict or keyword arguments,"
@@ -2570,7 +2592,8 @@ def wrapper(*args, **kwargs):
 # In 3.11, the ability to define generic `NamedTuple`s was supported.
 # This was explicitly disallowed in 3.9-3.10, and only half-worked in <=3.8.
 # On 3.12, we added __orig_bases__ to call-based NamedTuples
-if sys.version_info >= (3, 12):
+# On 3.13, we deprecated kwargs-based NamedTuples
+if sys.version_info >= (3, 13):
     NamedTuple = typing.NamedTuple
 else:
     def _make_nmtuple(name, types, module, defaults=()):
@@ -2614,8 +2637,11 @@ def __new__(cls, typename, bases, ns):
             )
             nm_tpl.__bases__ = bases
             if typing.Generic in bases:
-                class_getitem = typing.Generic.__class_getitem__.__func__
-                nm_tpl.__class_getitem__ = classmethod(class_getitem)
+                if hasattr(typing, '_generic_class_getitem'):  # 3.12+
+                    nm_tpl.__class_getitem__ = classmethod(typing._generic_class_getitem)
+                else:
+                    class_getitem = typing.Generic.__class_getitem__.__func__
+                    nm_tpl.__class_getitem__ = classmethod(class_getitem)
             # update from user namespace without overriding special namedtuple attributes
             for key in ns:
                 if key in _prohibited_namedtuple_fields:
@@ -2626,17 +2652,71 @@ def __new__(cls, typename, bases, ns):
                 nm_tpl.__init_subclass__()
             return nm_tpl
 
-    def NamedTuple(__typename, __fields=None, **kwargs):
-        if __fields is None:
-            __fields = kwargs.items()
+    def NamedTuple(__typename, __fields=_marker, **kwargs):
+        """Typed version of namedtuple.
+
+        Usage::
+
+            class Employee(NamedTuple):
+                name: str
+                id: int
+
+        This is equivalent to::
+
+            Employee = collections.namedtuple('Employee', ['name', 'id'])
+
+        The resulting class has an extra __annotations__ attribute, giving a
+        dict that maps field names to types.  (The field names are also in
+        the _fields attribute, which is part of the namedtuple API.)
+        An alternative equivalent functional syntax is also accepted::
+
+            Employee = NamedTuple('Employee', [('name', str), ('id', int)])
+        """
+        if __fields is _marker:
+            if kwargs:
+                deprecated_thing = "Creating NamedTuple classes using keyword arguments"
+                deprecation_msg = (
+                    "{name} is deprecated and will be disallowed in Python {remove}. "
+                    "Use the class-based or functional syntax instead."
+                )
+            else:
+                deprecated_thing = "Failing to pass a value for the 'fields' parameter"
+                example = f"`{__typename} = NamedTuple({__typename!r}, [])`"
+                deprecation_msg = (
+                    "{name} is deprecated and will be disallowed in Python {remove}. "
+                    "To create a NamedTuple class with 0 fields "
+                    "using the functional syntax, "
+                    "pass an empty list, e.g. "
+                ) + example + "."
+        elif __fields is None:
+            if kwargs:
+                raise TypeError(
+                    "Cannot pass `None` as the 'fields' parameter "
+                    "and also specify fields using keyword arguments"
+                )
+            else:
+                deprecated_thing = "Passing `None` as the 'fields' parameter"
+                example = f"`{__typename} = NamedTuple({__typename!r}, [])`"
+                deprecation_msg = (
+                    "{name} is deprecated and will be disallowed in Python {remove}. "
+                    "To create a NamedTuple class with 0 fields "
+                    "using the functional syntax, "
+                    "pass an empty list, e.g. "
+                ) + example + "."
         elif kwargs:
             raise TypeError("Either list of fields or keywords"
                             " can be provided to NamedTuple, not both")
+        if __fields is _marker or __fields is None:
+            warnings.warn(
+                deprecation_msg.format(name=deprecated_thing, remove="3.15"),
+                DeprecationWarning,
+                stacklevel=2,
+            )
+            __fields = kwargs.items()
         nt = _make_nmtuple(__typename, __fields, module=_caller())
         nt.__orig_bases__ = (NamedTuple,)
         return nt
 
-    NamedTuple.__doc__ = typing.NamedTuple.__doc__
     _NamedTuple = type.__new__(_NamedTupleMeta, 'NamedTuple', (), {})
 
     # On 3.8+, alter the signature so that it matches typing.NamedTuple.