Virtual environments are a useful way of separating dependencies and establishing a working environment for Python projects. The most common way of achieving this is through the use of virtualenv or pipenv. But since Python 3.3, a subset of virtualenv has been integrated into the standard library under the venv module. Though not as featureful as the former two, venv is a simple way of getting a functional virtual environment setup.
This gist was inspired by Corey Schafer's video on venv.
The commands are intended to be used on any Arch-based Linux distribution. For others distros, python3 and pip3 might be the way to go.
Since venv is a built-in module of any stock Python installation we don't need to install anything (apart from python-pip if it's not yet installed).
To create a virtual environment in the virtual_env folder:
python -m venv virtual_env
In order for the virtual environment to have access to globally installed Python packages the flag --system-site-packages should be used.
To activate the virtual environment
source virtual_env/bin/activate
This will add some text to your command prompt indicating that the environment is activated. The output of pip list should be different than the one we see without the virtual environment.
Typing which python will retrieve the path of the Python interpreter which the venv will use. The version of Python used in the virtual environment will be the same as the one that was installed in the system when the venv was created. If you REALLY need to use different Python versions you must use other solutions, like virtualenv.
To deactivate the virtual environment just type
deactivate
Packages can be installed with pip. These will exist only within the virtual environment and will not be accesible otherwise.
pip install package_name
We can generate a list of required packages so anybody can create an environment which uses the same requirements and dependencies (and the same versions).
pip freeze > requirements.txt
If the venv has access to globally installed packages and we only want to add locally installed packages to requirements.txt add the --local flag.
With the virtual environment activated we can install the packages in the requirements.txt file:
pip install -r requirements.txt
Probably a more modern way of handling virtual environments is using Pipenv and pipfiles. However I personally decided, by now, to stick with the method previously described for simplicity reasons.
Thank you for an honest summary of the issues involved. Personally, I think that a lot of the uncertainty derives from the difficulties one may experience in segmenting their work into separate projects. If you are in a world where you are working in teams and individuals are constantly changing, the management of these environments can be problematic.