Well, I certainly wouldn't call C++/Python interop
easy. It is, IMO, verbose, arcane and complex. BUT, once it works, you have truly seamless integration of Python and C++ code. It feels as magical as, say, two languages interacting on JVM or .NET (not that I used either). Or different languages talking through a REST API.
In C++, you'd write your C++ code as if you don't care about Python. Then, you add the "glue" code, which tells C++ how to convert objects to and from Python (there's more options than that but let's leave it here). That, plus a lot of boilerplate. Then, in effect, you can pass objects back and forth between Python and C++, create objects in C++, return them to Python, pass them back to more C++ functions, and so on.
I haven't used Nim+Python; but looking at Nimpy documentation, it looks like, for example, to export a class from Nim to Python, it needs to inherit from a special underlying class. You can't just take a class and make it available in Python. And even then, can you pass that back to Nim to call a function with?
Maybe yes, and if so, that bumps Nim higher up my priority list.