feat(spec): xarray data binder for math-spec programs

.github/workflows/test.yml

@@ -82,7 +82,7 @@ jobs:
     - name: Install package and dependencies
       run: |
         python -m pip install uv
-        uv pip install --system "$(ls dist/*.whl)[dev,solvers,oetc]"
+        uv pip install --system "$(ls dist/*.whl)[dev,solvers,oetc]" --group spec
 
     - name: Test with pytest
       env:

conftest.py

@@ -0,0 +1,9 @@
+"""Root pytest configuration for ``--doctest-modules`` collection of ``linopy/``."""
+
+from __future__ import annotations
+
+from importlib.util import find_spec
+
+collect_ignore: list[str] = []
+if find_spec("math_spec") is None:
+    collect_ignore.append("linopy/spec")

doc/contributing.rst

@@ -45,6 +45,9 @@ To run the test suite:
     # Install development dependencies
     uv sync --extra dev --extra solvers
 
+    # Also run the math-spec binder tests (needs Python >= 3.12)
+    uv sync --extra dev --extra solvers --group spec
+
     # Run all tests
     pytest
 

linopy/spec/__init__.py

@@ -0,0 +1,22 @@
+"""
+Build linopy models from math-spec programs.
+
+The package needs the ``math-spec`` distribution (import name ``math_spec``,
+Python >= 3.12). It is imported here and nowhere else in linopy, so
+``import linopy`` never pulls it in.
+"""
+
+from __future__ import annotations
+
+from importlib.util import find_spec
+
+if find_spec("math_spec") is None:
+    raise ImportError(
+        "linopy.spec needs the math-spec package. Install it with "
+        "`pip install math-spec` (Python >= 3.12) and try again."
+    )
+
+from linopy.spec.binder import Bound, Retain, bind
+from linopy.spec.errors import SpecDataError
+
+__all__ = ["Bound", "Retain", "SpecDataError", "bind"]