What's the difference between PDM and Virtual Envs?

[robml]

Is your feature request related to a problem? Please describe.

So I understand from using PDM it doesn't require to be "activated" in a virtual environment to use, I simply go to the project folder and can start using everything there with all my libraries also there. My question is, what is the difference from instantiating a "venv" in your project folder and holding everything there? I am still trying to understand how package managers work here. Also does PDM create a physical copy of each library or does it point to the existing library if it is already installed on the system? Would it not be more redundant to have the libraries stored per project if I can reuse a common set of libraries in a single virtual env that I can use across projects? These are just a few of my questions as I find myself trying to find a set up that works for myself and our team.

Describe the solution you'd like

Just trying to understand.

[pawamoy]

Functionally speaking (can wa say that in english?), using PDM or Poetry is not that different than explicitely using a virtualenv. Poetry hides it while PDM just does not use virtualenvs. The advantage I see in PDM is that you don't have to activate and deactivate your venv anymore (you just run pdm run ...), and you don't even have a virtualenv. It's simpler. Packages are available in the __pypackages__ folder and that's it, Python can find them.

Also does PDM create a physical copy of each library or does it point to the existing library if it is already installed on the system?

PDM has the install_cache feature which keeps installed packages in a cache folder, and create symlinks (or .pth files) to them in your __pypackages__ folder. It makes the installation faster, and saves tremendous amounts of space on your disk 🙂

[robml]

This is actually very intuitive thank you, I had no idea it worked in such a way. Is this cache folder somewhere else on the system I assume then? That way my symlinks can all point to the same place? All in all the above definitely seems to take care a lot for you then, and has made me appreciate PDM more.

[pawamoy]

On Linux the packages cache folder is located at ~/.cache/pdm/packages. PDM takes care of creating the symlinks when running pdm install. It's indeed one of the features that makes PDM so much more enjoyable than other alternatives ^^

[frostming]

I'd like to refer to several articles:

• https://frostming.com/2021/01-22/introducing-pdm/#the-problems-with-virtual-environments
• https://laike9m.com/blog/best-python-development-setup-for-2022-and-beyond,144/#pdm

[pawamoy]

@frostming I'll go ahead and move this to a discussion, let me know if you'd prefer I don't do that.

[robml]

Thank you for doing so, I had no idea the Discussions tab existed here. Seems more appropriate.