Python中setdefault()通过键查找字典中对应的值

以下Python代码中setdefault('d', 666)的返回值是什么？

myDic = {"a":1, "b":2, "c":3}
print("print(myDic): ",myDic)
print("print(myDic.setdefault('a', 666)): ",myDic.setdefault('a', 666))
print("print(myDic): ",myDic)
print("print(myDic.setdefault('d', 666)): ",myDic.setdefault('d', 666))
print("print(myDic): ",myDic)