Remove unused unique arg and fix empty parents

src/spikeinterface/core/node_pipeline.py

@@ -429,36 +429,59 @@ def compute(self, traces, peaks):
         return sparse_wfs
 
 
-def find_parent_of_type(list_of_parents, parent_type, unique=True):
+def find_parent_of_type(list_of_parents, parent_type):
+    """
+    Find a single parent of a given type(s) in a list of parents.
+    If multiple parents of the given type are found, the first parent is returned.
+
+    Parameters
+    ----------
+    list_of_parents : list of PipelineNode
+        List of parents to search through.
+    parent_type : type
+        The type of parent to search for.
+
+    Returns
+    -------
+    parent : PipelineNode or None
+        The parent of the given type. Returns None if no parent of the given type is found.
+    """
     if list_of_parents is None:
         return None
 
-    parents = []
-    for parent in list_of_parents:
-        if isinstance(parent, parent_type):
-            parents.append(parent)
+    parents = find_parents_of_type(list_of_parents, parent_type)
 
-    if unique and len(parents) == 1:
-        return parents[0]
-    elif not unique and len(parents) > 1:
+    if len(parents) > 0:
         return parents[0]
     else:
         return None
 
 
 def find_parents_of_type(list_of_parents, parent_type):
+    """
+    Find all parents of a given type(s) in a list of parents.
+
+    Parameters
+    ----------
+    list_of_parents : list of PipelineNode
+        List of parents to search through.
+    parent_type : type | tuple of types
+        The type(s) of parents to search for.
+
+    Returns
+    -------
+    parents : list of PipelineNode
+        List of parents of the given type(s). Returns an empty list if no parents of the given type(s) are found.
+    """
     if list_of_parents is None:
-        return None
+        return []
 
     parents = []
     for parent in list_of_parents:
         if isinstance(parent, parent_type):
             parents.append(parent)
 
-    if len(parents) > 0:
-        return parents
-    else:
-        return None
+    return parents
 
 
 def check_graph(nodes):
@@ -618,7 +641,6 @@ def _compute_peak_pipeline_chunk(segment_index, start_frame, end_frame, worker_c
     recording_segment = recording._recording_segments[segment_index]
     retrievers = find_parents_of_type(nodes, (SpikeRetriever, PeakRetriever))
     # get peak slices once for all retrievers
-    retriever_node = None
     peak_slice_by_retriever = {}
     for retriever in retrievers:
         peak_slice = i0, i1 = retriever.get_peak_slice(segment_index, start_frame, end_frame, max_margin)