The pex lockfile really is a beautiful thing! I'm working on splitting transitive version constraints out of my requirements files (I'll use https://www.pantsbuild.org/v2.14/docs/reference-python#resolves_to_constraints_file for the transitive dep constraints). As I'm going through, I ask "what requires package x?" (because I want to note that in my comment about why a transitve dep is constrained). I can search through the lockfile to very quickly see which things depend on which packages. When I've had to do things like this in the past, I sometimes ended up downloading wheels and inspecting them myself which was a royal pain.