Did you mean pyenv? pipenv is a package manager. You can specify in pipenv which version of Python your project needs, but to utilize it requires that that the version is already installed on your system.
> to utilize it requires that that the version is already installed on your system.
Almost correct. It requires either that the version is already on your system, or it can find an installation of pyenv configured in the standard way (and, on some quirky situations with OSX, configured but pristine--without any pre-existing Python builds). In the latter case, it'll ask you if you want it to automatically build and cache/install a Python of the specified version.