getdeps.py fails with pip and pex

[r-barnes]

Running

./build/fbcode_builder/getdeps.py install-system-deps --recursive fbthrift

on a minimal copy of Ubuntu 24.04 leads to two issues.

First, pip might not be installed. I fixed this with

sudo apt install python3-pip

Second, pip throws an error:

---
+ pip \
+      install \
+      pex
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
    python3-xyz, where xyz is the package you are trying to
    install.
    
    If you wish to install a non-Debian-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
    sure you have python3-full installed.
    
    If you wish to install a non-Debian packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.
    
    See /usr/share/doc/python3.12/README.venv for more information.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
Command '['pip', 'install', 'pex']' returned non-zero exit status 1.
!! Failed

I'm trying

sudo apt install python3-pex

instead.