Also, sorry to double post, but you don't actually need to activate the venv. You can just invoke `venv/bin/pip`. That should hopefully save you a bit of time and annoyance.
Firstly, non-experiences Python users (the kind who need recipes to follow) will also blindly follow installation instructions on websites. These all say "pip install xxx" and users will inevitably forget they need to change the path to make that work for their environment. By getting into the habit of activating the environment this problem goes away.
Secondly, you do need to activate the venv so that command line tools in ./venv/bin are used (instead of whatever is in your default path).
This includes both the correct version of python (if you set it when you setup the virtual environment) and importantly jupyter. From personal experience there's a whole set of pain when you don't realize your jupyter isn't the one inside the virtual environment and so is using other libraries.
Because many shells cache the location of executables, if you don't deactivate and reactivate your virtual environment after installing Jupyter into it then it may (in some circumstances) use a globally installed version.
