v3 and v4 compatibility

[MainRo]

Hello there,

I am porting some packages to rxpy4 and would like to support both rxpy v3 and v4. So far this seems straightforward in the code, but I do not see how to express this in setuptools:
How can I declare in my setup.py that I depend either on "reactive>=4", or "rx>=3"?

[MainRo]

For information, I tested making my code compatible with both versions by conditioning the imports this way:

try:
    import reactivex as rx
except ModuleNotFoundError:
    import rx

but it clutters the code too much. Moreover, I did not find a way to express the dependency. So in my case, I will bump to v4.