📝 Updated docstring

tests/test_extensions.py

@@ -81,12 +81,24 @@ def arc_dummy_patch():
     assert (
         model.nodes[node.name].apply_overrides.__qualname__ == dummy_patch.__qualname__
     )
+    assert (
+        model.nodes[node.name]._patched_apply_overrides.__qualname__
+        == "Node.apply_overrides"
+    )
     assert model.nodes[node.name].t == another_dummy_patch(node)
-    assert model.nodes[node.name].pull_set_handler["default"] == yet_another_dummy_patch
+    assert model.nodes[node.name]._patched_t == None
+    assert (
+        model.nodes[node.name].pull_set_handler["default"].__qualname__
+        == yet_another_dummy_patch.__qualname__
+    )
     assert (
         model.nodes[node.name].dummy_arc.arc_mass_balance.__qualname__
         == arc_dummy_patch.__qualname__
     )
+    assert (
+        model.nodes[node.name].dummy_arc._patched_arc_mass_balance.__qualname__
+        == "Arc.arc_mass_balance"
+    )
 
 
 def assert_dict_almost_equal(d1: dict, d2: dict, tol: float | None = None):

wsimod/extensions.py

@@ -39,7 +39,13 @@
 
 It should be noted that the patched function should have the same signature as the
 original method or attribute, and the return type should be the same as well, otherwise
-there will be a runtime error.
+there will be a runtime error. In particular, the first argument of the patched function
+should be the node object itself, which will typically be named `self`.
+
+The overridden method or attribute can be accessed within the patched function using the
+`_patched_{method_name}` attribute of the object, eg. `self._patched_pull_distributed`. 
+The exception to this is when patching an item, in which case the original item is no
+available to be used within the overriding function.
 
 Finally, the `apply_patches` is called within the `Model.load` method and will apply all
 patches in the order they were registered. This means that users need to be careful with
@@ -110,10 +116,9 @@ def apply_patches(model: Model) -> None:
         # Apply the patch
         if item is not None:
             obj = getattr(obj, method)
-            obj[item] = func(node) if is_attr else func
+            obj[item] = func(node) if is_attr else func.__get__(obj, obj.__class__)
         else:
-            if is_attr:
-                setattr(obj, method, func(node))
-            else:
-                setattr(obj, f"_patched_{method}", getattr(obj, method))
-                setattr(obj, method, func.__get__(obj, obj.__class__))
+            setattr(obj, f"_patched_{method}", getattr(obj, method))
+            setattr(
+                obj, method, func(node) if is_attr else func.__get__(obj, obj.__class__)
+            )