bpo-37049: PEP 589: Add TypedDict to typing module (GH-13573)

The implementation is straightforward and essentially is just copied from `typing_extensions`.

Doc/library/typing.rst

@@ -878,6 +878,39 @@ The module defines the following classes, functions and decorators:
       The ``_field_types`` and ``__annotations__`` attributes are
       now regular dictionaries instead of instances of ``OrderedDict``.
 
+.. class:: TypedDict(dict)
+
+   A simple typed namespace. At runtime it is equivalent to
+   a plain :class:`dict`.
+
+   ``TypedDict`` creates a dictionary type that expects all of its
+   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.
+   Usage::
+
+      class Point2D(TypedDict):
+          x: int
+          y: int
+          label: str
+
+      a: Point2D = {'x': 1, 'y': 2, 'label': 'good'}  # OK
+      b: Point2D = {'z': 3, 'label': 'bad'}           # Fails type check
+
+      assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')
+
+   The type info for introspection can be accessed via ``Point2D.__annotations__``
+   and ``Point2D.__total__``.  To allow using this feature with older versions
+   of Python that do not support :pep:`526`, ``TypedDict`` supports two additional
+   equivalent syntactic forms::
+
+      Point2D = TypedDict('Point2D', x=int, y=int, label=str)
+      Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
+
+   See :pep:`589` for more examples and detailed rules of using ``TypedDict``
+   with type checkers.
+
+   .. versionadded:: 3.8
 
 .. function:: NewType(typ)
 

Lib/test/test_typing.py

@@ -18,7 +18,7 @@ from typing import get_type_hints
 from typing import no_type_check, no_type_check_decorator
 from typing import Type
 from typing import NewType
-from typing import NamedTuple
+from typing import NamedTuple, TypedDict
 from typing import IO, TextIO, BinaryIO
 from typing import Pattern, Match
 import abc
@@ -1883,6 +1883,18 @@ class XRepr(NamedTuple):
     def __add__(self, other):
         return 0
 
+Label = TypedDict('Label', [('label', str)])
+
+class Point2D(TypedDict):
+    x: int
+    y: int
+
+class LabelPoint2D(Point2D, Label): ...
+
+class Options(TypedDict, total=False):
+    log_level: int
+    log_path: str
+
 class HasForeignBaseClass(mod_generics_cache.A):
     some_xrepr: 'XRepr'
     other_a: 'mod_generics_cache.A'
@@ -2658,6 +2670,97 @@ class XMethBad2(NamedTuple):
             self.assertEqual(jane2, jane)
 
 
+class TypedDictTests(BaseTestCase):
+    def test_basics_functional_syntax(self):
+        Emp = TypedDict('Emp', {'name': str, 'id': int})
+        self.assertIsSubclass(Emp, dict)
+        self.assertIsSubclass(Emp, typing.MutableMapping)
+        self.assertNotIsSubclass(Emp, collections.abc.Sequence)
+        jim = Emp(name='Jim', id=1)
+        self.assertIs(type(jim), dict)
+        self.assertEqual(jim['name'], 'Jim')
+        self.assertEqual(jim['id'], 1)
+        self.assertEqual(Emp.__name__, 'Emp')
+        self.assertEqual(Emp.__module__, __name__)
+        self.assertEqual(Emp.__bases__, (dict,))
+        self.assertEqual(Emp.__annotations__, {'name': str, 'id': int})
+        self.assertEqual(Emp.__total__, True)
+
+    def test_basics_keywords_syntax(self):
+        Emp = TypedDict('Emp', name=str, id=int)
+        self.assertIsSubclass(Emp, dict)
+        self.assertIsSubclass(Emp, typing.MutableMapping)
+        self.assertNotIsSubclass(Emp, collections.abc.Sequence)
+        jim = Emp(name='Jim', id=1)
+        self.assertIs(type(jim), dict)
+        self.assertEqual(jim['name'], 'Jim')
+        self.assertEqual(jim['id'], 1)
+        self.assertEqual(Emp.__name__, 'Emp')
+        self.assertEqual(Emp.__module__, __name__)
+        self.assertEqual(Emp.__bases__, (dict,))
+        self.assertEqual(Emp.__annotations__, {'name': str, 'id': int})
+        self.assertEqual(Emp.__total__, True)
+
+    def test_typeddict_errors(self):
+        Emp = TypedDict('Emp', {'name': str, 'id': int})
+        self.assertEqual(TypedDict.__module__, 'typing')
+        jim = Emp(name='Jim', id=1)
+        with self.assertRaises(TypeError):
+            isinstance({}, Emp)
+        with self.assertRaises(TypeError):
+            isinstance(jim, Emp)
+        with self.assertRaises(TypeError):
+            issubclass(dict, Emp)
+        with self.assertRaises(TypeError):
+            TypedDict('Hi', x=1)
+        with self.assertRaises(TypeError):
+            TypedDict('Hi', [('x', int), ('y', 1)])
+        with self.assertRaises(TypeError):
+            TypedDict('Hi', [('x', int)], y=int)
+
+    def test_py36_class_syntax_usage(self):
+        self.assertEqual(LabelPoint2D.__name__, 'LabelPoint2D')
+        self.assertEqual(LabelPoint2D.__module__, __name__)
+        self.assertEqual(LabelPoint2D.__annotations__, {'x': int, 'y': int, 'label': str})
+        self.assertEqual(LabelPoint2D.__bases__, (dict,))
+        self.assertEqual(LabelPoint2D.__total__, True)
+        self.assertNotIsSubclass(LabelPoint2D, typing.Sequence)
+        not_origin = Point2D(x=0, y=1)
+        self.assertEqual(not_origin['x'], 0)
+        self.assertEqual(not_origin['y'], 1)
+        other = LabelPoint2D(x=0, y=1, label='hi')
+        self.assertEqual(other['label'], 'hi')
+
+    def test_pickle(self):
+        global EmpD  # pickle wants to reference the class by name
+        EmpD = TypedDict('EmpD', name=str, id=int)
+        jane = EmpD({'name': 'jane', 'id': 37})
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            z = pickle.dumps(jane, proto)
+            jane2 = pickle.loads(z)
+            self.assertEqual(jane2, jane)
+            self.assertEqual(jane2, {'name': 'jane', 'id': 37})
+            ZZ = pickle.dumps(EmpD, proto)
+            EmpDnew = pickle.loads(ZZ)
+            self.assertEqual(EmpDnew({'name': 'jane', 'id': 37}), jane)
+
+    def test_optional(self):
+        EmpD = TypedDict('EmpD', name=str, id=int)
+
+        self.assertEqual(typing.Optional[EmpD], typing.Union[None, EmpD])
+        self.assertNotEqual(typing.List[EmpD], typing.Tuple[EmpD])
+
+    def test_total(self):
+        D = TypedDict('D', {'x': int}, total=False)
+        self.assertEqual(D(), {})
+        self.assertEqual(D(x=1), {'x': 1})
+        self.assertEqual(D.__total__, False)
+
+        self.assertEqual(Options(), {})
+        self.assertEqual(Options(log_level=2), {'log_level': 2})
+        self.assertEqual(Options.__total__, False)
+
+
 class IOTests(BaseTestCase):
 
     def test_io(self):

Lib/typing.py

@@ -89,6 +89,7 @@ __all__ = [
     'Set',
     'FrozenSet',
     'NamedTuple',  # Not really a type.
+    'TypedDict',  # Not really a type.
     'Generator',
 
     # One-off things.
@@ -1490,6 +1491,89 @@ class NamedTuple(metaclass=NamedTupleMeta):
         return _make_nmtuple(typename, fields)
 
 
+def _dict_new(cls, *args, **kwargs):
+    return dict(*args, **kwargs)
+
+
+def _typeddict_new(cls, _typename, _fields=None, **kwargs):
+    total = kwargs.pop('total', True)
+    if _fields is None:
+        _fields = kwargs
+    elif kwargs:
+        raise TypeError("TypedDict takes either a dict or keyword arguments,"
+                        " but not both")
+
+    ns = {'__annotations__': dict(_fields), '__total__': total}
+    try:
+        # Setting correct module is necessary to make typed dict classes pickleable.
+        ns['__module__'] = sys._getframe(1).f_globals.get('__name__', '__main__')
+    except (AttributeError, ValueError):
+        pass
+
+    return _TypedDictMeta(_typename, (), ns)
+
+
+def _check_fails(cls, other):
+    # Typed dicts are only for static structural subtyping.
+    raise TypeError('TypedDict does not support instance and class checks')
+
+
+class _TypedDictMeta(type):
+    def __new__(cls, name, bases, ns, total=True):
+        """Create new typed dict class object.
+
+        This method is called directly when TypedDict is subclassed,
+        or via _typeddict_new when TypedDict is instantiated. This way
+        TypedDict supports all three syntax forms described in its docstring.
+        Subclasses and instances of TypedDict return actual dictionaries
+        via _dict_new.
+        """
+        ns['__new__'] = _typeddict_new if name == 'TypedDict' else _dict_new
+        tp_dict = super(_TypedDictMeta, cls).__new__(cls, name, (dict,), ns)
+
+        anns = ns.get('__annotations__', {})
+        msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
+        anns = {n: _type_check(tp, msg) for n, tp in anns.items()}
+        for base in bases:
+            anns.update(base.__dict__.get('__annotations__', {}))
+        tp_dict.__annotations__ = anns
+        if not hasattr(tp_dict, '__total__'):
+            tp_dict.__total__ = total
+        return tp_dict
+
+    __instancecheck__ = __subclasscheck__ = _check_fails
+
+
+class TypedDict(dict, metaclass=_TypedDictMeta):
+    """A simple typed namespace. At runtime it is equivalent to a plain dict.
+
+    TypedDict creates a dictionary type that expects all of its
+    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.
+    Usage::
+
+        class Point2D(TypedDict):
+            x: int
+            y: int
+            label: str
+
+        a: Point2D = {'x': 1, 'y': 2, 'label': 'good'}  # OK
+        b: Point2D = {'z': 3, 'label': 'bad'}           # Fails type check
+
+        assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')
+
+    The type info can be accessed via Point2D.__annotations__. TypedDict
+    supports two additional equivalent forms::
+
+        Point2D = TypedDict('Point2D', x=int, y=int, label=str)
+        Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
+
+    The class syntax is only supported in Python 3.6+, while two other
+    syntax forms work for Python 2.7 and 3.2+
+    """
+
+
 def NewType(name, tp):
     """NewType creates simple unique types with almost zero
     runtime overhead. NewType(name, tp) is considered a subtype of tp

Misc/NEWS.d/next/Library/2019-05-25-19-48-42.bpo-37049.an2LXJ.rst

@@ -0,0 +1 @@
+PEP 589: Add ``TypedDict`` to the ``typing`` module.