pip install fails with 'error: externally-managed-environment' (This environment is externally managed) on Debian 12, Ubuntu 23.04+, Homebrew Python or Fedora. What's the right fix?

Cause: PEP 668 lets an operating system mark its own Python as managed by the system package manager. When the file EXTERNALLY-MANAGED is present in the standard library directory, pip (23.0 and later) refuses to install into that interpreter, so pip can't break tools the OS depends on. Debian 12, Ubuntu 23.04 and later, recent Fedora, Homebrew's Python and some Docker base images ship this marker. It shows up most often in scripts and Dockerfiles that ran 'pip install' globally and worked on older images. Fix (best first): 1. Use a virtual environment for project dependencies: python3 -m venv .venv . .venv/bin/activate (Windows: .venv\Scripts\activate) pip install -r requirements.txt On Debian/Ubuntu you may first need: sudo apt install python3-venv (or python3.X-venv). 2. For command-line tools you want available everywhere (black, httpie, ruff and so on), use pipx install <tool>; it gives each tool its own environment. 3. If the OS packages the library, install it with the package manager instead (for example apt install python3-requests). 4. In Docker, either create a venv in the image and put its bin directory first on PATH, or use an official python:3.x image, whose interpreter is not marked as externally managed. 5. Last resort only: pip install --break-system-packages (or PIP_BREAK_SYSTEM_PACKAGES=1). It can overwrite files the OS relies on and break system tools; don't use it with sudo on a workstation. Deleting the EXTERNALLY-MANAGED file has the same risk. Verify: which python and which pip point inside .venv (or the pipx tool runs), and pip install succeeds without the flag. Sources: https://peps.python.org/pep-0668/ https://packaging.python.org/en/latest/specifications/externally-managed-environments/ https://docs.python.org/3/library/venv.html