OrderedDict的主要目的是保留创建元素的顺序。
你想要的是 collections.Counter ，内置了最常见的功能：

The primary purpose of OrderedDict is retaining the order in which the elements were created. What you want here is collections.Counter, which has the n-most-frequent functionality built-in:

>>> dictionary={'a':10,'b':20,'c':30,'d':5}
>>> import collections
>>> collections.Counter(dictionary).most_common(2)
[('c', 30), ('b', 20)]