[zeptomu]

The problem is that accessing shared state concurrently in a multi-process context is a non-trivial problem, so specific software emerged that handles these problems for you.

The simplest solution is to use a small DB system like sqlite. It is built into Python (import sqlite3) performs reasonably well and you do not have to run an additional service.

Now if a small DB like sqlite already feels overblown to you (and it really is simple and small) you might not need concurrent access either, so the simplest solution is to just use a file where you store your state.

[icebraining]

I'd say the simplest solution is a global (or just shared) variable using a thread-safe container like queue.Queue. There's also multiprocessing.Queue, which supports sharing the queue across multiple workers.