Add warning for experimental node access API

src/oemof/network/energy_system.py

@@ -23,6 +23,8 @@
 import blinker
 import dill as pickle
 
+from oemof.tools import debugging
+
 from oemof.network.groupings import DEFAULT as BY_UID
 from oemof.network.groupings import Entities
 from oemof.network.groupings import Grouping
@@ -195,6 +197,11 @@ def groups(self):
 
     @property
     def node(self):
+        msg = (
+            "The API to access nodes by label is experimental"
+            " and might change without prior notice."
+        )
+        warnings.warn(msg, debugging.ExperimentalFeatureWarning)
         return self._nodes
 
     @property

tests/test_energy_system.py

@@ -54,6 +54,14 @@ def test_add_nodes(self):
         assert node2 in self.es.nodes
         assert (node1, node2) in self.es.flows().keys()
 
+    def test_node_access_warning(self):
+        node_label = "label"
+        self.es.add(Node(node_label))
+        with pytest.warns(
+            match='API to access nodes by label is experimental'
+        ):
+            _ = es.node[node_label]
+
     def test_add_flow_assignment(self):
         assert not self.es.nodes