Detemine source for update in separate function

src/ert/analysis/_es_update.py

@@ -470,6 +470,23 @@ def _split_by_batchsize(
     return np.array_split(arr, sections)
 
 
+def _determine_parameter_source(
+    param_group_name: str, target_fs: EnsembleAccessor, source_fs: EnsembleReader
+) -> Union[EnsembleReader, EnsembleAccessor]:
+    """
+    Determines the source for a parameter group based on whether it is available in `target_fs`.
+    It is possible to update the same parameter multiple times.
+    For example, two update steps may be defined where one udpates the parameter using observation
+    `A` while the other udpates it using observation `B`.
+    After the processing of the first update step has completed, the updated parameter is stored in `traget_fs`.
+    Hence, when processing the second update step, we need to load the parameter from `target_fs` and not `source_fs`.
+    """
+    if target_fs.has_parameter_group(param_group_name):
+        return target_fs
+    else:
+        return source_fs
+
+
 def _update_with_row_scaling(
     update_step: UpdateStep,
     source_fs: EnsembleReader,
@@ -485,10 +502,7 @@ def _update_with_row_scaling(
 ) -> None:
     for param_group in update_step.row_scaling_parameters:
         source: Union[EnsembleReader, EnsembleAccessor]
-        if target_fs.has_parameter_group(param_group.name):
-            source = target_fs
-        else:
-            source = source_fs
+        source = _determine_parameter_source(param_group.name, target_fs, source_fs)
         temp_storage = _create_temporary_parameter_storage(
             source, iens_active_index, param_group.name
         )
@@ -637,10 +651,7 @@ def adaptive_localization_progress_callback(
 
         for param_group in update_step.parameters:
             source: Union[EnsembleReader, EnsembleAccessor]
-            if target_fs.has_parameter_group(param_group.name):
-                source = target_fs
-            else:
-                source = source_fs
+            source = _determine_parameter_source(param_group.name, target_fs, source_fs)
             temp_storage = _create_temporary_parameter_storage(
                 source, iens_active_index, param_group.name
             )
@@ -837,13 +848,7 @@ def analysis_IES(
         sies_smoother.W[:, masking_of_initial_parameters] = proposed_W
 
         for param_group in update_step.parameters:
-            source: Union[EnsembleReader, EnsembleAccessor] = target_fs
-            try:
-                target_fs.load_parameters(group=param_group.name, realizations=0)[
-                    "values"
-                ]
-            except Exception:
-                source = source_fs
+            source = _determine_parameter_source(param_group.name, target_fs, source_fs)
             temp_storage = _create_temporary_parameter_storage(
                 source, iens_active_index, param_group.name
             )