support pickling a linopy model

Signed-off-by: Victor Garcia Reolid <victor@seita.nl>

Author: Victor Garcia Reolid

linopy/constraints.py

@@ -755,6 +755,9 @@ def __getattr__(self, name: str) -> Constraint:
         raise AttributeError(
             f"Constraints has no attribute `{name}` or the attribute is not accessible, e.g. raises an error."
         )
+    
+    def __getstate__(self): return self.__dict__
+    def __setstate__(self, d): return self.__dict__.update(d)
 
     def __dir__(self) -> list[str]:
         base_attributes = list(super().__dir__())

linopy/variables.py

@@ -1181,6 +1181,9 @@ def __getattr__(self, name: str) -> Variable:
         raise AttributeError(
             f"Variables has no attribute `{name}` or the attribute is not accessible / raises an error."
         )
+    
+    def __getstate__(self): return self.__dict__
+    def __setstate__(self, d): return self.__dict__.update(d)
 
     def __dir__(self) -> list[str]:
         base_attributes = list(super().__dir__())

test/test_io.py

@@ -11,6 +11,7 @@
 import pandas as pd
 import pytest
 import xarray as xr
+import pickle
 
 from linopy import LESS_EQUAL, Model, available_solvers, read_netcdf
 from linopy.testing import assert_model_equal
@@ -108,6 +109,20 @@ def test_model_to_netcdf_with_status_and_condition(
 
     assert_model_equal(m, p)
 
+def test_pickle_model(model_with_dash_names: Model, tmp_path: Path):
+    m = model_with_dash_names
+    fn = tmp_path / "test.nc"
+    m._status = "ok"
+    m._termination_condition = "optimal"
+
+    with open(fn, 'wb') as f:
+        pickle.dump(m, f)
+
+    with open(fn, 'rb') as f:
+        p = pickle.load(f)
+
+    assert_model_equal(m, p)
+
 
 # skip it xarray version is 2024.01.0 due to issue https://github.com/pydata/xarray/issues/8628
 @pytest.mark.skipif(