Python app to organise ideas by tags
Have two dictionaries:

Idea -> Set of Tags
Tag -> Set of Ideas

When you add a new idea, add it to the first dictionary, and then update all the sets of the tags it uses in the second dictionary. This way you get easy lookup by both tag and idea.
Please give me a hint about how is it better to code a Python application which helps to organise ideas by tags. 
Add a new idea:
Input 1: the idea
Input 2: corresponding tags
Search for the idea:
Input 1: one or multiple tags
As far as I understood, it's necessary to create an array with ideas and an array with tags. But how to connect them? For example, idea number 3 corresponds to tags number 1 and 2. So the question is: how to link these two arrays in the most simple and elegant way?