I find it best to keep virtual envs completely away from the project (I use http://virtualenvwrapper.readthedocs.org/en/latest/ which puts them by default in ~/.virtualenvs). A virtualenv is completely machine-specific.
If your project is a package itself (i.e. it has a setup.py file), then use that file to specify dependencies. On a new machine I check out a copy, create a virtual env and activate it. Then in the local copy I run "pip install -e .". This installs all the requirements from setup.py in the virtualenv, and links the local copy of my project to it as well. Now your package is available in the virtual env, but fully editable.
If your python project is not a package, you can install its dependencies in a virtual env with pip. Then run "pip freeze" to generate a list of all installed packages. Save that to a text file in your repository, e.g. ``requirements.txt``. On a different machine, or a fresh venv, you can then do "pip install -r requirements.txt" to set everything up in one go.
Alright, so after I set up the environment using pip and virtualenv, I see it has python in it, etc. If I use pip freeze > requirements.txt, it lists the packages I have installed using pip, but it doesn't list anything for the python version itself. How do I make sure the right python version gets captured if I don't check in the /env/ folder?
I think this works well as a convention even if you're not deploying to Heroku. I also like the suggestion to put a guard in setup.py that checks sys.version_info.
If your project is a package itself (i.e. it has a setup.py file), then use that file to specify dependencies. On a new machine I check out a copy, create a virtual env and activate it. Then in the local copy I run "pip install -e .". This installs all the requirements from setup.py in the virtualenv, and links the local copy of my project to it as well. Now your package is available in the virtual env, but fully editable.
If your python project is not a package, you can install its dependencies in a virtual env with pip. Then run "pip freeze" to generate a list of all installed packages. Save that to a text file in your repository, e.g. ``requirements.txt``. On a different machine, or a fresh venv, you can then do "pip install -r requirements.txt" to set everything up in one go.