REF: simplify Index.take, MultiIndex.take (pandas-dev#37551)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -740,44 +740,36 @@ def take(self, indices, axis=0, allow_fill=True, fill_value=None, **kwargs):
         if kwargs:
             nv.validate_take(tuple(), kwargs)
         indices = ensure_platform_int(indices)
-        if self._can_hold_na:
-            taken = self._assert_take_fillable(
-                self._values,
-                indices,
-                allow_fill=allow_fill,
-                fill_value=fill_value,
-                na_value=self._na_value,
-            )
-        else:
-            if allow_fill and fill_value is not None:
-                cls_name = type(self).__name__
-                raise ValueError(
-                    f"Unable to fill values because {cls_name} cannot contain NA"
-                )
-            taken = self._values.take(indices)
+        allow_fill = self._maybe_disallow_fill(allow_fill, fill_value, indices)
+
+        # Note: we discard fill_value and use self._na_value, only relevant
+        #  in the case where allow_fill is True and fill_value is not None
+        taken = algos.take(
+            self._values, indices, allow_fill=allow_fill, fill_value=self._na_value
+        )
         return self._shallow_copy(taken)
 
-    def _assert_take_fillable(
-        self, values, indices, allow_fill=True, fill_value=None, na_value=np.nan
-    ):
+    def _maybe_disallow_fill(self, allow_fill: bool, fill_value, indices) -> bool:
         """
-        Internal method to handle NA filling of take.
+        We only use pandas-style take when allow_fill is True _and_
+        fill_value is not None.
         """
-        indices = ensure_platform_int(indices)
-
-        # only fill if we are passing a non-None fill_value
         if allow_fill and fill_value is not None:
-            if (indices < -1).any():
+            # only fill if we are passing a non-None fill_value
+            if self._can_hold_na:
+                if (indices < -1).any():
+                    raise ValueError(
+                        "When allow_fill=True and fill_value is not None, "
+                        "all indices must be >= -1"
+                    )
+            else:
+                cls_name = type(self).__name__
                 raise ValueError(
-                    "When allow_fill=True and fill_value is not None, "
-                    "all indices must be >= -1"
+                    f"Unable to fill values because {cls_name} cannot contain NA"
                 )
-            taken = algos.take(
-                values, indices, allow_fill=allow_fill, fill_value=na_value
-            )
         else:
-            taken = algos.take(values, indices, allow_fill=False, fill_value=na_value)
-        return taken
+            allow_fill = False
+        return allow_fill
 
     _index_shared_docs[
         "repeat"

pandas/core/indexes/multi.py

@@ -2018,29 +2018,13 @@ def __getitem__(self, key):
     def take(self, indices, axis=0, allow_fill=True, fill_value=None, **kwargs):
         nv.validate_take(tuple(), kwargs)
         indices = ensure_platform_int(indices)
-        taken = self._assert_take_fillable(
-            self.codes,
-            indices,
-            allow_fill=allow_fill,
-            fill_value=fill_value,
-            na_value=-1,
-        )
-        return MultiIndex(
-            levels=self.levels, codes=taken, names=self.names, verify_integrity=False
-        )
 
-    def _assert_take_fillable(
-        self, values, indices, allow_fill=True, fill_value=None, na_value=None
-    ):
-        """ Internal method to handle NA filling of take """
         # only fill if we are passing a non-None fill_value
-        if allow_fill and fill_value is not None:
-            if (indices < -1).any():
-                msg = (
-                    "When allow_fill=True and fill_value is not None, "
-                    "all indices must be >= -1"
-                )
-                raise ValueError(msg)
+        allow_fill = self._maybe_disallow_fill(allow_fill, fill_value, indices)
+
+        na_value = -1
+
+        if allow_fill:
             taken = [lab.take(indices) for lab in self.codes]
             mask = indices == -1
             if mask.any():
@@ -2052,7 +2036,10 @@ def _assert_take_fillable(
                 taken = masked
         else:
             taken = [lab.take(indices) for lab in self.codes]
-        return taken
+
+        return MultiIndex(
+            levels=self.levels, codes=taken, names=self.names, verify_integrity=False
+        )
 
     def append(self, other):
         """