Check with inspect.routine()

src/decorator.py

@@ -71,7 +71,7 @@ def __init__(self, func=None, name=None, signature=None,
                 self.name = '_lambda_'
             self.doc = func.__doc__
             self.module = func.__module__
-            if inspect.isfunction(func):
+            if inspect.isroutine(func):
                 argspec = getfullargspec(func)
                 self.annotations = getattr(func, '__annotations__', {})
                 for a in ('args', 'varargs', 'varkw', 'defaults', 'kwonlyargs',