How to classify English words according to topics with python? Such as THE COUNTRY AND GOVERNMENT: regime, politically, politician, official, democracy......besides, there are other topics: education/family/economy/subjects and so on.

I want to sort out *The Economist* magazine vocabularies and classify these **according to frequency and topic.** 
At present, I have completed the words frequency statistics, the next step is how to classify these words automatically with python?