On 24/02/2021 19.17, Steve Dower wrote: > On 2/24/2021 4:26 PM, Christian Heimes wrote: >> On 24/02/2021 15.16, Random832 wrote: >>> On Wed, Feb 24, 2021, at 06:27, Christian Heimes wrote: >>>> Separate directories don't prevent clashes and system breakage. But >>>> they >>>> provide an easy way to *recover* from a broken system. >>> >>> I think it could be turned into a way to prevent them by A) having >>> site-packages always take precedence over dist-packages [i believe >>> this is already the case] in normal usage and B) providing an option >>> to the interpreter, used by system scripts, to exclude site-packages >>> entirely from the path. >>> >>> Basically, site-packages would effectively be layered on top of "Lib >>> + dist-packages" in a similar way to how a venv is layered on top of >>> the main python installation - the inverse of the suggestion someone >>> else in the thread made for the system python to be a venv. This >>> wouldn't *exactly* be a venv because it wouldn't imply the other >>> things that entering a venv does such as "python" [and script names >>> such as pip] being an alias for the correct version of python, but it >>> would provide the same kind of one-way isolation, whereby the "system >>> environment" can influence the "normal environment" and not >>> vice-versa, in the same way that packages installed in the main >>> installation affect a venv [unless system-site-packages is disabled] >>> but the venv obviously has no effect on the main installati > on. >> >> Yes, you are describing one major aspect of my idea for a system Python >> interpreter. I'm happy to read that other users are coming to similar >> conclusions. Instead of an option I'd create a new executable to lock >> down additional things (e.g. isolated mode, code verification hook). A >> separate executable would also allow distros to provide a stripped down >> interpreter that does not cause bad user experience. > > I mean, this is _precisely_ what PEP 370 defines (including the "-s" > option and PYTHONNOUSERSITE env variable to provide that one-way > isolation). > > Is the problem that pip doesn't use it by default? Or that the distros > went and made patches for the runtime rather than patching pip? (For > Windows installs from the Store, where even admin rights can't do an > all-users package install, I added a new config file location for pip to > change this default, but a patch would also have worked.) > > Maybe we need an easier way to patch the location of user site packages? > I also had to do this for the Store install on Windows, and it's a > little bit of a hack... but maybe having an official recommendation > would help encourage distributors to use the mechanism?
(sorry for terse reply, I'm heading out.) Linux distros want an additional layer so the can differentiate between Python packages installed by their package manager and Python packages installed with "sudo pip install". Python has two default site-package directories (from highest to lowest precedence): 1. ~/.local/lib/python3.9/site-packages 2. /usr/lib/python3.9/site-packages (1) is defined by site.getusersitepackages(), (2) site.getsitepackages() Linux distro have additional site-package directories. My Fedora system X86_64 system with multiarch has three additional candidates. 1. ~/.local/lib/python3.9/site-packages 2. /usr/local/lib64/python3.9/site-packages 3. /usr/local/lib/python3.9/site-packages 4. /usr/lib64/python3.9/site-packages 5. /usr/lib/python3.9/site-packages The "lib" directories are for pure Python packages whiel the "lib64" directories contain X86_64 native code extensions (aka shared libraries). The "/usr/lib*" directories are used for distro packages. The downstream patch [1] ensures that "sudo pip install" installs packages into "/usr/local/lib". AFAIK "/usr/local/lib64" is not used. Debian has a similar mechanism to provide "/usr/lib/python3/dist-packages" [2]. A hypothetical /usr/bin/system-python3 interpreter would only use (4) and (5) as site-package directories. A user-facing /usr/bin/python3 would use (1) to (5). Christian [1] https://src.fedoraproject.org/rpms/python3.9/blob/rawhide/f/00251-change-user-install-location.patch [2] https://www.debian.org/doc/packaging-manuals/python-policy/ch-python.html _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/RZACFNIDET7FZJG6LC25EAPWCR7ADFUE/ Code of Conduct: http://python.org/psf/codeofconduct/
