len()：容器中项目数量
Return the length (the number of items) of an object. The argument may be a sequence (string, tuple or list) or a mapping (dictionary).
__sizeof__()：返回对象的内存大小。 比len()多了一个垃圾收集器开销
Return the size of an object in bytes. The object can be any type of object. All built-in objects will return correct results, but this does not have to hold true for third-party extensions as it is implementation specific.
getsizeof() calls the object’s __sizeof__ method and adds an additional garbage collector overhead if the object is managed by the garbage collector.