Add support for typing.Annotated (Issue #19)

runtype/pytypes.py

@@ -364,6 +364,9 @@ def _to_canon(self, t):
         if isinstance(t, tuple):
             return SumType([to_canon(x) for x in t])
 
+        if hasattr(typing, '_AnnotatedAlias') and isinstance(t, typing._AnnotatedAlias):
+            return to_canon(t.__origin__)
+
         try:
             t.__origin__
         except AttributeError:
@@ -418,7 +421,6 @@ def _to_canon(self, t):
             elif t.__origin__ is abc.Sequence or t.__origin__ is typing.Sequence:
                 x ,= t.__args__
                 return Sequence[to_canon(x)]
-
             elif t.__origin__ is type or t.__origin__ is typing.Type:
                 # TODO test issubclass on t.__args__
                 return PythonDataType(type)

tests/test_basic.py

@@ -87,9 +87,17 @@ def test_basic(self):
         assert not isa(frozenset({'a'}), FrozenSet[int])
         assert not isa(frozenset({'a'}), Set[int])
 
+
     def test_basic2(self):
         assert issubclass(List[Tuple], list)
 
+        if hasattr(typing, 'Annotated'):
+            a = typing.Annotated[int, range(1, 10)]
+            assert is_subtype(a, int)
+            assert is_subtype(int, a)
+            assert isa(1, a)
+
+
     def test_assert(self):
         assert_isa(1, int)
         assert_isa("a", str)