How to locate a virtualenv install
Why not start checking what processes are actually running, and with what commandline, using ps auxf or something of the sort. Then you know if its nginx+uwsgi or django-devserver or what, and maybe even see the virtualenv path, if it's being launched very manually. Then, look at the config file of the server you find.
Alternatively, look around, using netstat -taupen, for example, which processes are listening to which ports. Makes even more sense, if there's a reverse proxy like nginx or whatever running, and you know that it's proxying to.
The requirements.txt I'd ignore completely. You'll get the same, but correct information from the virtualenv once you activate it and run pip freeze. The file's superfluous at best, and misleading at worst.
Btw, if this old contractor compiled and installed a custom Python, (s)he might not even have used a virtualenv, while still avoiding the system libraries and PYTHONPATH. Unlikely, but possible.
Deploying to a live server for an existing Django application. It's a very old site that has not been updated in 3+ years. 
I was hired on contract to bring it up to date, which included upgrading the Django version to be current. This broke many things on the site that had to be repaired.
I did a test deployment and it went fine. Now it is time for deployment to live and I am having some issues....
First thing I was going to do is keep a log of the current Django version on server, incase of any issues we can roll back. I tried logging in Python command prompt and importing Django to find version number, and it said Django not found.
I was looking further and found the version in a pip requirements.txt file. 
Then I decided to update the actual django version on the server. Update went through smoothly. Then I checked the live site, and everything was unchanged (with the old files still in place). Most of the site should have been broken. It was not recognizing any changes in Django.
I am assuming the reason for this might be that the last contractor used virtualenv? And that's why it is not recognizing Django, or the Django update are not doing anything to the live site?
That is the only reason I could come up with to explain this issue, as since there is a pip requirements.txt file, he likely installed Django with pip, which means Python should recognize the path to Django. 
So then I was going to try to find the source path for the virtualenv with command "lsvirtualenv". But when I do that, even that gives me a "command not found" error.
My only guess is that this was an older version of virtualenv that does not have this command? If that is not the case, I'm not sure what is going on.
Any advice for how I find the information I need to  update the package versions on this server with the tools I have access to?