Without the change the eval fails as:
$ nix build --no-link -f. pythonInterpreters.pypy310_prebuilt.tests.test-packageOverrides
error:
… in the condition of the assert statement
at pkgs/development/interpreters/python/tests.nix:212:11:
211| in
212| assert myPython.pkgs.foobar == myPython.pkgs.numpy;
| ^
213| myPython.withPackages (ps: with ps; [ foobar ]);
… while evaluating the attribute 'outPath'
at lib/customisation.nix:421:7:
420| drv.drvPath;
421| outPath =
| ^
422| assert condition;
(stack trace truncated; use '--show-trace' to show the full, detailed trace)
error: attribute 'mainProgram' missing
at pkgs/by-name/me/meson/package.nix:75:52:
74| --replace-fail "PythonExternalProgram('python3', mesonlib.python_command)" \
75| "PythonExternalProgram('${python3.meta.mainProgram}', mesonlib.python_command)"
| ^
76| substituteInPlace mesonbuild/modules/python3.py \