Creating a requirements.txt after installation
pip freeze > requirements.txt is the canonical way to capture all the packages you have installed in a Python project. I am not sure why; it doesn't do what you expect.
Laughs in Javascript
Coming from Javascript I am still amazed by how primitive the DX in python feels in comparison. If you use pip, there is no pnpm add PACKAGE or npm i PACKAGE --save to install a package and save a reference into the requirements.txt. Of course poetry creates lock files automatically, but pip is the standard python package manager, it should do the right thing. Instead, after installing packages with pip install PACKAGEA PACKAGEB ... one has to capture the installed packages with pip freeze > requirements.txt. At least that’s what popular search engines tell you to do.
In reality, pip install PACKAGEA PACKAGEB followed by pip freeze > requirements.txt can potentially generate a requirements.txt which is quite long. That’s because freeze is giving you a snapshot of the packages installed in your environment, not the one you meant to install. When pip installs PACKAGEA PACKAGEB, it also installs all of their dependencies. All of these dependencies will then be listed in your requirements.txt. But what you really want to do is just have a requirements like
PACKAGEA==4.0.1
PACKAGEB==1.0.3For that you need to install a separate tool.
Enter pipreqs
There are actually different tools for doing this; in my experience they are interchangeable, and I wouldn’t agonise about which one to choose. I picked pipreqs because it was the first I came across, but pip-compile works just as well. I installed it with pipx so that is available globally. Of course, I had to install pipx first
❯ brew install pipx
==> Auto-updating Homebrew...
...
❯ pipx install pipreqs
installed package pipreqs 0.5.0, installed using Python 3.12.3
...
❯ pipreqs . --force
...
INFO: Successfully saved requirements file in ./requirements.txtAnd that’s the gist of it.