This guide discusses how to install packages using pip and a virtual environment manager: either venv for Python 3 or virtualenv for Python 2. These are the lowest-level tools for managing Python packages and are recommended if higher-level tools do not suit your needs.
Well, a virtual environment is just a directory with three important components:
A site-packages/ folder where third party libraries are installed.
Symlinks to Python executables installed on your system.
Scripts that ensure executed Python code uses the Python interpreter and site packages installed inside the given virtual environment.
(venv) % pip freeze numpy==1.15.3
And write the output to a file, which we’ll call requirements.txt.
(venv) % pip freeze > requirements.txt
Duplicating Environments
Sara% cd test-project/ Sara% python3 -m venv venv/ (venv) Sara% pip install -r requirements.txtCollecting numpy==1.15.3 (from -r i (line 1)) Installing collected packages: numpy Successfully installed numpy-1.15.3
…python -m pip executes pip using the Python interpreter you specified as python. So /usr/bin/python3.7 -m pip means you are executing pip for your interpreter located at /usr/bin/python3.7.
But when you use python -m pip with python being the specific interpreter you want to use, all of the above ambiguity is gone. If I say python3.8 -m pip then I know pip will be using and installing for my Python 3.8 interpreter (same goes for if I had said python3.7).
While we’re on the subject of how to avoid messing up your Python installation, I want to make the point that you should never install stuff into your global Python interpreter when you. develop locally (containers are a different matter)! If it’s your system install of Python then you may actually break your system if you install an incompatible version of a library that your OS relies on.
