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gh-105570: Deprecate unusual ways of creating empty TypedDicts (#105780) · python/cpython@7b1f0f2 · GitHub

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AlexWaygood
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gh-105570: Deprecate unusual ways of creating empty TypedDicts (#105780)
Deprecate two methods of creating typing.TypedDict classes with 0 fields using the functional syntax: `TD = TypedDict("TD")` and `TD = TypedDict("TD", None)`. Both will be disallowed in Python 3.15. To create a TypedDict class with 0 fields, either use `class TD(TypedDict): pass` or `TD = TypedDict("TD", {})`.
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‎Doc/library/typing.rst‎

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@@ -2388,6 +2388,14 @@ These are not used in annotations. They are building blocks for declaring types.
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.. versionchanged:: 3.13
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Removed support for the keyword-argument method of creating ``TypedDict``\ s.
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.. deprecated-removed:: 3.13 3.15
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When using the functional syntax to create a TypedDict class, failing to
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pass a value to the 'fields' parameter (``TD = TypedDict("TD")``) is
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deprecated. Passing ``None`` to the 'fields' parameter
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(``TD = TypedDict("TD", None)``) is also deprecated. Both will be
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disallowed in Python 3.15. To create a TypedDict class with 0 fields,
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use ``class TD(TypedDict): pass`` or ``TD = TypedDict("TD", {})``.
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Protocols
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---------
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‎Doc/whatsnew/3.13.rst‎

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@@ -146,12 +146,15 @@ Deprecated
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be disallowed in Python 3.15. Use the class-based syntax or the functional
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syntax instead. (Contributed by Alex Waygood in :gh:`105566`.)
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* When using the functional syntax to create a :class:`typing.NamedTuple`
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class, failing to pass a value to the 'fields' parameter
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(``NT = NamedTuple("NT")``) is deprecated. Passing ``None`` to the 'fields'
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parameter (``NT = NamedTuple("NT", None)``) is also deprecated. Both will be
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disallowed in Python 3.15. To create a NamedTuple class with 0 fields, use
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``class NT(NamedTuple): pass`` or ``NT = NamedTuple("NT", [])``.
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(Contributed by Alex Waygood in :gh:`105566`.)
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class or a :class:`typing.TypedDict` class, failing to pass a value to the
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'fields' parameter (``NT = NamedTuple("NT")`` or ``TD = TypedDict("TD")``) is
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deprecated. Passing ``None`` to the 'fields' parameter
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(``NT = NamedTuple("NT", None)`` or ``TD = TypedDict("TD", None)``) is also
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deprecated. Both will be disallowed in Python 3.15. To create a NamedTuple
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class with 0 fields, use ``class NT(NamedTuple): pass`` or
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``NT = NamedTuple("NT", [])``. To create a TypedDict class with 0 fields, use
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``class TD(TypedDict): pass`` or ``TD = TypedDict("TD", {})``.
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(Contributed by Alex Waygood in :gh:`105566` and :gh:`105570`.)
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* :mod:`array`'s ``'u'`` format code, deprecated in docs since Python 3.3,
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emits :exc:`DeprecationWarning` since 3.13

‎Lib/test/test_typing.py‎

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@@ -7823,6 +7823,40 @@ class MultipleGenericBases(GenericParent[int], GenericParent[float]):
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self.assertEqual(MultipleGenericBases.__orig_bases__, (GenericParent[int], GenericParent[float]))
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self.assertEqual(CallTypedDict.__orig_bases__, (TypedDict,))
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def test_zero_fields_typeddicts(self):
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T1 = TypedDict("T1", {})
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class T2(TypedDict): pass
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class T3[tvar](TypedDict): pass
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S = TypeVar("S")
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class T4(TypedDict, Generic[S]): pass
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expected_warning = re.escape(
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"Failing to pass a value for the 'fields' parameter is deprecated "
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"and will be disallowed in Python 3.15. "
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"To create a TypedDict class with 0 fields "
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"using the functional syntax, "
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"pass an empty dictionary, e.g. `T5 = TypedDict('T5', {})`."
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)
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with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
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T5 = TypedDict('T5')
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expected_warning = re.escape(
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"Passing `None` as the 'fields' parameter is deprecated "
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"and will be disallowed in Python 3.15. "
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"To create a TypedDict class with 0 fields "
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"using the functional syntax, "
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"pass an empty dictionary, e.g. `T6 = TypedDict('T6', {})`."
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)
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with self.assertWarnsRegex(DeprecationWarning, fr"^{expected_warning}$"):
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T6 = TypedDict('T6', None)
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for klass in T1, T2, T3, T4, T5, T6:
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with self.subTest(klass=klass.__name__):
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self.assertEqual(klass.__annotations__, {})
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self.assertEqual(klass.__required_keys__, set())
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self.assertEqual(klass.__optional_keys__, set())
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self.assertIsInstance(klass(), dict)
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class RequiredTests(BaseTestCase):
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‎Lib/typing.py‎

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@@ -2908,7 +2908,7 @@ def __subclasscheck__(cls, other):
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__instancecheck__ = __subclasscheck__
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def TypedDict(typename, fields=None, /, *, total=True):
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def TypedDict(typename, fields=_sentinel, /, *, total=True):
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"""A simple typed namespace. At runtime it is equivalent to a plain dict.
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TypedDict creates a dictionary type such that a type checker will expect all
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See PEP 655 for more details on Required and NotRequired.
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"""
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if fields is None:
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if fields is _sentinel or fields is None:
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import warnings
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if fields is _sentinel:
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deprecated_thing = "Failing to pass a value for the 'fields' parameter"
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else:
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deprecated_thing = "Passing `None` as the 'fields' parameter"
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example = f"`{typename} = TypedDict({typename!r}, {{{{}}}})`"
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deprecation_msg = (
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"{name} is deprecated and will be disallowed in Python {remove}. "
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"To create a TypedDict class with 0 fields "
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"using the functional syntax, "
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"pass an empty dictionary, e.g. "
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) + example + "."
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warnings._deprecated(deprecated_thing, message=deprecation_msg, remove=(3, 15))
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fields = {}
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ns = {'__annotations__': dict(fields)}

‎Misc/NEWS.d/next/Library/2023-06-14-14-32-31.gh-issue-105570.sFTtQU.rst‎

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Deprecate two methods of creating :class:`typing.TypedDict` classes with 0
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fields using the functional syntax: ``TD = TypedDict("TD")`` and
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``TD = TypedDict("TD", None)``. Both will be disallowed in Python 3.15. To create a
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``TypedDict`` class with 0 fields, either use ``class TD(TypedDict): pass``
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or ``TD = TypedDict("TD", {})``.

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