Suppose, not entirely hypothetically, that you need to create a new Python 2 virtual environment today; perhaps you need to install some package to see how its old Python 2 version behaves. With Python 3, creating a virtual environment is really easy; it's just 'python3 -m venv /tmp/pytest'. With Python 2 today, you have two complications. First, Python 2 doesn't have a venv module (instead it uses a 'virtualenv' command), and second, your installed Python 2 environment may not have all of the necessary infrastructure already set up since people are deprecating Python 2 and cutting down any OS provided version of it to the bare minimum.

First, you need a Python 2 version of pip. Hopefully you have one already; if not, you want the 2.7 version of get-pip.py, but don't count on that URL lasting forever, as the URL in my 2021 entry on this didn't. I haven't tested this latest version, so cross your fingers. If you still care at all about Python 2, you probably really want to make sure you have a pip2 at this point.

Once you have a pip2 in one way or another, you want to do a user install of 'virtualenv', with 'pip2 install --user virtualenv'. This will give you a ~/.local/bin/virtualenv command, which you may want to rename to 'virtualenv2'. You can then use this to create your virtual environment, 'virtualenv2 /tmp/pytest'. The result should normally have everything you need to use the virtualenv, including a pip2, and you can then use this virtualenv pip2 to install the package or packages you need to poke at.

Incidentally, if you just want to get a copy of the Python 2 version of a particular package and not specifically install it somewhere, you can just use pip2 to download it, with 'pip2 download <whatever>'. I'm not sure that the result is necessarily immediately usable and you'll have to decode it yourself ('file' may be your friend), but depending on what you want this may be good enough.

(I took a quick look to see if there was an easier way to find out the last supported Python 2 version of a package than 'pip2 download <whatever>', but as far as I can see there isn't.)

(This is one of the entries that I write for myself so that I have this information if I ever need it again, although I certainly hope not to.)

PS: Another option is to use the Python 2.7 version of PyPy, which I believe comes pre-set with its own pip2, although not its own already installed virtualenv. Depending on how concerned you are about differences in behavior between CPython 2.7 and PyPy 2.7, this might not be a good option.