CLN: setops (#42228)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -3089,8 +3089,6 @@ def _intersection(self, other: Index, sort=False):
         """
         intersection specialized to the case with matching dtypes.
         """
-        # TODO(EA): setops-refactor, clean all this up
-
         if self.is_monotonic and other.is_monotonic:
             try:
                 result = self._inner_indexer(other)[0]
@@ -3109,6 +3107,7 @@ def _wrap_intersection_result(self, other, result):
         # We will override for MultiIndex to handle empty results
         return self._wrap_setop_result(other, result)
 
+    @final
     def _intersection_via_get_indexer(self, other: Index, sort) -> ArrayLike:
         """
         Find the intersection of two Indexes using get_indexer.
@@ -3184,9 +3183,10 @@ def difference(self, other, sort=None):
             return self.rename(result_name)
 
         result = self._difference(other, sort=sort)
-        return self._wrap_setop_result(other, result)
+        return self._wrap_difference_result(other, result)
 
     def _difference(self, other, sort):
+        # overridden by RangeIndex
 
         this = self.unique()
 
@@ -3199,6 +3199,11 @@ def _difference(self, other, sort):
 
         return the_diff
 
+    def _wrap_difference_result(self, other, result):
+        # We will override for MultiIndex to handle empty results
+        return self._wrap_setop_result(other, result)
+
+    @final
     def symmetric_difference(self, other, result_name=None, sort=None):
         """
         Compute the symmetric difference of two Index objects.
@@ -3246,6 +3251,16 @@ def symmetric_difference(self, other, result_name=None, sort=None):
 
         if result_name is not None:
             result = result.rename(result_name)
+
+        if self._is_multi and len(result) == 0:
+            # On equal symmetric_difference MultiIndexes the difference is empty.
+            # Therefore, an empty MultiIndex is returned GH#13490
+            return type(self)(
+                levels=[[] for _ in range(self.nlevels)],
+                codes=[[] for _ in range(self.nlevels)],
+                names=result.names,
+            )
+
         return result
 
     @final

pandas/core/indexes/multi.py

@@ -3552,7 +3552,7 @@ def _maybe_match_names(self, other):
         return names
 
     def _wrap_intersection_result(self, other, result):
-        other, result_names = self._convert_can_do_setop(other)
+        _, result_names = self._convert_can_do_setop(other)
 
         if len(result) == 0:
             return MultiIndex(
@@ -3564,20 +3564,18 @@ def _wrap_intersection_result(self, other, result):
         else:
             return MultiIndex.from_arrays(zip(*result), sortorder=0, names=result_names)
 
-    def _difference(self, other, sort) -> MultiIndex:
-        other, result_names = self._convert_can_do_setop(other)
-
-        difference = super()._difference(other, sort)
+    def _wrap_difference_result(self, other, result):
+        _, result_names = self._convert_can_do_setop(other)
 
-        if len(difference) == 0:
+        if len(result) == 0:
             return MultiIndex(
                 levels=[[]] * self.nlevels,
                 codes=[[]] * self.nlevels,
                 names=result_names,
                 verify_integrity=False,
             )
         else:
-            return MultiIndex.from_tuples(difference, sortorder=0, names=result_names)
+            return MultiIndex.from_tuples(result, sortorder=0, names=result_names)
 
     def _convert_can_do_setop(self, other):
         result_names = self.names
@@ -3599,18 +3597,6 @@ def _convert_can_do_setop(self, other):
 
         return other, result_names
 
-    def symmetric_difference(self, other, result_name=None, sort=None):
-        # On equal symmetric_difference MultiIndexes the difference is empty.
-        # Therefore, an empty MultiIndex is returned GH13490
-        tups = Index.symmetric_difference(self, other, result_name, sort)
-        if len(tups) == 0:
-            return type(self)(
-                levels=[[] for _ in range(self.nlevels)],
-                codes=[[] for _ in range(self.nlevels)],
-                names=tups.names,
-            )
-        return tups
-
     # --------------------------------------------------------------------
 
     @doc(Index.astype)