I have two python packages ([locust-swarm](https://github.com/SvenskaSpel/locust-swarm/) and [locust-plugins](https://github.com/SvenskaSpel/locust-plugins/)). Neither has a strict requirement to the other, but they can work together, and my users install them separately.

Sometimes there is a breaking change in one or the other, and I want to make sure nobody installs incompatible versions (by updating package A but not package B, for example). Is there a way to specify a minimum version of this "pseudo-dependency" and fail the install if it is not satisfied? A check that is *only done if the other package is already installed*.

I do *not* want to add one package as a dependency of the other and force users of package A to install package B, just to be able to handle this case.

Probably this question has been asked before, but I couldnt find an answer.