How do I add a feature in Python 3 where objects will spawn on their own?

So, I've been working on-and-off on a side-project for a few weeks now. I now want to add an automatic spawning system, like how objects can spawn in Minecraft without being instantiated in the code. I already have a few classes ready. How would I do this?

Andrew 01.12.2017

If this were Stack Overflow I'd mark your question as "should be closed" because "too broad".

Is this a real-time game? Do you know how to count how many seconds have passed? Can you implement a loop that calls a function after X seconds have passed?

Chris 02.12.2017