デコレータで関数に属性を付与

def note(**kw):
    def applier(func):
        __notes__ = getattr(func, '__notes__', None)
        if __notes__ is None:
            __notes__ = dict()
            setattr(func, '__notes__', __notes__)
        __notes__.update(kw)
        return func
    return applier

@note(foo='this is add')
@note(bar='加算')
def add(a, b):
    return a + b

print('add(10, 20) ->', add(10, 20))
print('add.__notes__ ->', add.__notes__)

$ python hoge.py
add(10, 20) -> 30
add.__notes__ -> {'bar': '加算', 'foo': 'this is add'}