Make starting layout variable names plural

The starting layout is a list and can have more than one entry. To make
this clearer, this commit renames starting_layout -> starting_layouts
and sabre_starting_layout -> sabre_starting_layouts.

Author: mtreinish

qiskit/transpiler/passes/layout/sabre_layout.py

@@ -76,10 +76,10 @@ class SabreLayout(TransformationPass):
 
     In addition to starting with a random initial `Layout` the pass can also take in
     an additional list of starting layouts which will be used for additional
-    trials. If the ``sabre_starting_layout`` is present in the property set
+    trials. If the ``sabre_starting_layouts`` is present in the property set
     when this pass is run, that will be used for additional trials. There will still
     be ``layout_trials`` of full random starting layouts run and the contents of
-    ``sabre_starting_layout`` will be run in addition to those. The output which results
+    ``sabre_starting_layouts`` will be run in addition to those. The output which results
     in the lowest amount of swap gates (whether from the random trials or the property
     set starting point) will be used. The value for this property set field should be a
     list of :class:`.Layout` objects representing the starting layouts to use. If a
@@ -89,7 +89,7 @@ class SabreLayout(TransformationPass):
     Property Set Fields Read
     ------------------------
 
-    ``sabre_starting_layout`` (``list[Layout]``)
+    ``sabre_starting_layouts`` (``list[Layout]``)
         An optional list of :class:`~.Layout` objects to use for additional layout trials. This is
         in addition to the full random trials specified with the ``layout_trials`` argument.
 
@@ -261,9 +261,9 @@ def run(self, dag):
         else:
             target = self.coupling_map
         inner_run = self._inner_run
-        if "sabre_starting_layout" in self.property_set:
+        if "sabre_starting_layouts" in self.property_set:
             inner_run = functools.partial(
-                self._inner_run, starting_layout=self.property_set["sabre_starting_layout"]
+                self._inner_run, starting_layouts=self.property_set["sabre_starting_layouts"]
             )
         components = disjoint_utils.run_pass_over_connected_components(dag, target, inner_run)
         self.property_set["layout"] = Layout(
@@ -346,7 +346,7 @@ def run(self, dag):
         disjoint_utils.combine_barriers(mapped_dag, retain_uuid=False)
         return mapped_dag
 
-    def _inner_run(self, dag, coupling_map, starting_layout=None):
+    def _inner_run(self, dag, coupling_map, starting_layouts=None):
         if not coupling_map.is_symmetric:
             # deepcopy is needed here to avoid modifications updating
             # shared references in passes which require directional
@@ -357,11 +357,11 @@ def _inner_run(self, dag, coupling_map, starting_layout=None):
         dist_matrix = coupling_map.distance_matrix
         original_qubit_indices = {bit: index for index, bit in enumerate(dag.qubits)}
         partial_layouts = []
-        if starting_layout is not None:
+        if starting_layouts is not None:
             coupling_map_reverse_mapping = {
                 coupling_map.graph[x]: x for x in coupling_map.graph.node_indices()
             }
-            for layout in starting_layout:
+            for layout in starting_layouts:
                 virtual_bits = layout.get_virtual_bits()
                 out_layout = [None] * len(dag.qubits)
                 for bit, phys in virtual_bits.items():