Overload '+' operator to concatenate ConfigSet objects

.github/workflows/pytests.yml

@@ -281,7 +281,7 @@ jobs:
           mpirun -n 2 pytest --cov=wfl --cov-report term --cov-config=tests/.coveragerc --cov-report term-missing --cov-report term:skip-covered --with-mpi -k mpi --cov-append
 
       - name: 'Upload Coverage Data'
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         if: env.coverage-on-version == matrix.python-version
         with:
           name: coverage-html-${{ matrix.python-version }}

tests/test_configset.py

@@ -263,6 +263,9 @@ def test_from_mult_ConfigSets(tmp_path, ats):
     locs = [f" / {i0} / {i1}" for i0 in range(3) for i1 in range(3)]
     check_ConfigSet(ConfigSet([cs_01, cs_2]), locs, gather_numbers([ats_i_0, ats_i_1, ats_i_2]))
 
+    # same check for overloaded + operator
+    check_ConfigSet(cs_01 + cs_2, locs, gather_numbers([ats_i_0, ats_i_1, ats_i_2]))
+
 def test_from_ConfigSets_mixed_0(tmp_path, ats):
     ats_i_0 = ats[0:3]
     ats_i_1 = ats[3:6]

wfl/configset.py

@@ -388,6 +388,12 @@ def _flat_iter(items):
                     yield at
 
 
+    def __add__(self, other):
+        if not isinstance(other, ConfigSet):
+            raise TypeError(f"unsupported operand type(s) for +: 'ConfigSet' and '{type(other)}'")
+        return ConfigSet([self, other])
+
+
 class OutputSpec:
     """Abstraction for writing to a ConfigSet, preserving tree structure.