Don't try to wrap generators that are untyped. (#118)

Co-authored-by: Alex Hall <alex.mojaki@gmail.com>

tests/test_typeguard.py

@@ -573,6 +573,16 @@ def generate(a: int):
         gen = generate(1)
         next(gen)
 
+    def test_wrapped_generator_no_return_type_annotation(self):
+        """Test that return type checking works in a generator function too."""
+        @typechecked
+        def generate(a: int):
+            yield a
+            yield a + 1
+
+        gen = generate(1)
+        next(gen)
+
     def test_varargs(self):
         def foo(*args: int):
             assert check_argument_types()

typeguard/__init__.py

@@ -825,11 +825,12 @@ def wrapper(*args, **kwargs):
         # If a generator is returned, wrap it if its yield/send/return types can be checked
         if inspect.isgenerator(retval) or isasyncgen(retval):
             return_type = memo.type_hints.get('return')
-            origin = getattr(return_type, '__origin__')
-            if origin in generator_origin_types:
-                return TypeCheckedGenerator(retval, memo)
-            elif origin is not None and origin in asyncgen_origin_types:
-                return TypeCheckedAsyncGenerator(retval, memo)
+            if return_type:
+                origin = getattr(return_type, '__origin__', None)
+                if origin in generator_origin_types:
+                    return TypeCheckedGenerator(retval, memo)
+                elif origin is not None and origin in asyncgen_origin_types:
+                    return TypeCheckedAsyncGenerator(retval, memo)
 
         return retval