[alexey-salmin]

Yes. But then any transitive dependency stays there forever even when not needed anymore.

Initial requirements (only first level, version ranges) and dependency resolution results (all transitive packages, exact versions or hashes) are two very different things and should be treated separately.

You can implement and maintain it by hand with two requirements.txt files but it's rarely done this way. And really at this level you're better off with a normal package manager.