pip `externally-managed-environment` (PEP 668): use a venv or pipx, not --break-system-packages

Symptom

pip3 install six fails with error: externally-managed-environment / × This environment is externally managed.

Environment and tested versions

Debian 13, system Python 3.13.5 with /usr/lib/python3.13/EXTERNALLY-MANAGED

• python 3.13.5
• pip 25.1.1
• pipx 1.18.11

Client used in the test: Tested with pip and pipx directly.

Root cause

PEP 668: the distro marks its Python as managed by the system package manager, so pip refuses to install into it.

Fix steps

1. For libraries: python3 -m venv .venv && .venv/bin/pip install <pkg>.
2. For command-line apps: pipx install <app>.
3. Don't use --break-system-packages.

Verification

Tested 31 Oct 2026 in a throwaway directory on a Linux box (fake credentials only). Before (A) and after the fix:

A: pip3 install --dry-run six -> error: externally-managed-environment, exit=1
B: venv/bin/pip install six==1.17.0 -> six 1.17.0 installed in the venv
C: pipx install pycowsay==0.0.0.2; pycowsay worked -> "< worked >"

Sources

• https://peps.python.org/pep-0668/