Python: building an LRU cache

I have around 6,00,000 entries in MongoDB in the following format:

feature:category:count

where

• feature could be any word,
• category is positive or negative, and
• count tells how many times a feature occurred in a document for that category.

I want to cache the top 1000 tuples, let's say so as not to query database each time.

How does one build an LRU cache in Python? Or are there any known solutions to this?