8000 gh-133823: require explicit empty sequence for 0-field `TypedDict` ob… · python/cpython@8731211 · GitHub
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gh-133823: require explicit empty sequence for 0-field TypedDict objects (#133863)
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‎Doc/whatsnew/3.15.rst

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@@ -137,6 +137,12 @@ typing
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Use the class-based syntax or the functional syntax instead.
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(Contributed by Bénédikt Tran in :gh:`133817`.)
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* Using ``TD = TypedDict("TD")`` or ``TD = TypedDict("TD", None)`` to
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construct a :class:`~typing.TypedDict` type with zero field is no
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longer supported. Use ``class TD(TypedDict): pass``
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or ``TD = TypedDict("TD", {})`` instead.
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(Contributed by Bénédikt Tran in :gh:`133823`.)
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140146

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Porting to Python 3.15
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======================

‎Lib/test/test_typing.py

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@@ -8853,39 +8853,27 @@ class MultipleGenericBases(GenericParent[int], GenericParent[float]):
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self.assertEqual(CallTypedDict.__orig_bases__, (TypedDict,))
88548854

88558855
def test_zero_fields_typeddicts(self):
8856-
T1 = TypedDict("T1", {})
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T1a = TypedDict("T1a", {})
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T1b = TypedDict("T1b", [])
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T1c = TypedDict("T1c", ())
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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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8862-
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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for klass in T1a, T1b, T1c, T2, T3, T4:
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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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def test_errors(self):
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with self.assertRaisesRegex(TypeError, "missing 1 required.*argument"):
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TypedDict('TD')
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with self.assertRaisesRegex(TypeError, "object is not iterable"):
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TypedDict('TD', None)
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def test_readonly_inheritance(self):
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class Base1(TypedDict):
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a: ReadOnly[int]

‎Lib/typing.py

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@@ -3159,7 +3159,7 @@ def __subclasscheck__(cls, other):
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__instancecheck__ = __subclasscheck__
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def TypedDict(typename, fields=_sentinel, /, *, total=True):
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def TypedDict(typename, fields, /, *, 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
@@ -3214,24 +3214,6 @@ class DatabaseUser(TypedDict):
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username: str # the "username" key can be changed
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"""
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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)}
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module = _caller()
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if module is not None:

‎Misc/NEWS.d/next/Library/2025-05-11-08-48-55.gh-issue-133823.F8udQy.rst

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@@ -0,0 +1,3 @@
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Remove support for ``TD = TypedDict("TD")`` and ``TD = TypedDict("TD", None)``
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calls for constructing :class:`typing.TypedDict` objects with zero field.
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Patch by Bénédikt Tran.

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