Fixed unwarranted TypeError when run within exec() (#210)

src/typeguard/__init__.py

@@ -351,7 +351,8 @@ def function_name(func: Callable) -> str:
 
     """
     # For partial functions and objects with __call__ defined, __qualname__ does not exist
-    module = getattr(func, '__module__', '')
+    # For functions run in `exec` with a custom namespace, __module__ can be None
+    module = getattr(func, '__module__', '') or ''
     qualname = (module + '.') if module not in ('builtins', '') else ''
     return qualname + getattr(func, '__qualname__', repr(func))
 

tests/test_typeguard.py

@@ -148,6 +148,19 @@ def test_check_recursive_type():
               r'List\[JSONType\], Dict\[str, JSONType\]\); got dict instead')
 
 
+def test_exec_no_namespace():
+    from textwrap import dedent
+
+    exec(dedent("""
+        from typeguard import typechecked
+
+        @typechecked
+        def f():
+            pass
+
+        """), {})
+
+
 class TestCheckArgumentTypes:
     def test_any_type(self):
         def foo(a: Any):