After #30527, it is possible to install Python packages built by the Sage distribution into user-defined venvs.

In this ticket, we create build/pkgs/sagelib/src/requirements.txt -> src/requirements.txt to facilitate installing sagelib into such a venv. (This file duplicates some information also available in build/pkgs; #29041 will rectify this.)

A virtual environment using it can be created and doctested using:

./sage -sh -c '(cd build/pkgs/sagelib/src && tox -v -v -v)'

(Reusing wheels built by the Sage distribution requires to do sage -i pip2pi first - this is from #30527.)

Related:

• Developer's Guide: Add instructions for sagelib development in a conda environment #28746 Developer's Guide: Add instructions for sagelib development in a conda environment
• Meta-ticket: Make sagelib pip-installable in a conda environment #28752 Make sagelib pip-installable in a conda environment

Follow-up tickets:

• Use pipenv to create venv for development #30371 In-place (editable) installs of sagelib in a venv
• sage_bootstrap: Add command "sage -package list --output={install-requires,requirements,pipfile,debian,....}" #29041 at ./bootstrap time, generate requirements.txt, constraints.txt, setup.cfg [install_requires], Pipfile from build/pkgs
• add documentation on how to set up the virtual environment, using either plain python -m venv, virtualenv (20.x), or pipenv.

Depends on #30527
Depends on #30013

CC: @tobiasdiez @kiwifb @jhpalmieri @videlec

Component: build

Keywords: sd111

Branch/Commit: u/mkoeppe/add-src-requirements-txt @ 9ad6b36

Issue created by migration from https://trac.sagemath.org/ticket/30578