REF: turn _try_mi into MultiIndex._get_values_for_loc (#31736)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -4597,7 +4597,7 @@ def get_value(self, series: "Series", key):
             else:
                 raise
 
-        return self._get_values_for_loc(series, loc)
+        return self._get_values_for_loc(series, loc, key)
 
     def _should_fallback_to_positional(self) -> bool:
         """
@@ -4607,12 +4607,14 @@ def _should_fallback_to_positional(self) -> bool:
             return False
         return True
 
-    def _get_values_for_loc(self, series: "Series", loc):
+    def _get_values_for_loc(self, series: "Series", loc, key):
         """
         Do a positional lookup on the given Series, returning either a scalar
         or a Series.
 
         Assumes that `series.index is self`
+
+        key is included for MultiIndex compat.
         """
         if is_integer(loc):
             return series._values[loc]

pandas/core/indexes/multi.py

@@ -1,5 +1,15 @@
 from sys import getsizeof
-from typing import Any, Hashable, Iterable, List, Optional, Sequence, Tuple, Union
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Hashable,
+    Iterable,
+    List,
+    Optional,
+    Sequence,
+    Tuple,
+    Union,
+)
 import warnings
 
 import numpy as np
@@ -56,6 +66,9 @@
     pprint_thing,
 )
 
+if TYPE_CHECKING:
+    from pandas import Series  # noqa:F401
+
 _index_doc_kwargs = dict(ibase._index_doc_kwargs)
 _index_doc_kwargs.update(
     dict(klass="MultiIndex", target_klass="MultiIndex or list of tuples")
@@ -2326,28 +2339,32 @@ def get_value(self, series, key):
             # We have to explicitly exclude generators, as these are hashable.
             raise InvalidIndexError(key)
 
-        def _try_mi(k):
-            # TODO: what if a level contains tuples??
-            loc = self.get_loc(k)
-
-            new_values = series._values[loc]
-            if is_scalar(loc):
-                return new_values
-
-            new_index = self[loc]
-            new_index = maybe_droplevels(new_index, k)
-            return series._constructor(
-                new_values, index=new_index, name=series.name
-            ).__finalize__(self)
-
         try:
-            return _try_mi(key)
+            loc = self.get_loc(key)
         except KeyError:
             if is_integer(key):
-                return series._values[key]
+                loc = key
             else:
                 raise
 
+        return self._get_values_for_loc(series, loc, key)
+
+    def _get_values_for_loc(self, series: "Series", loc, key):
+        """
+        Do a positional lookup on the given Series, returning either a scalar
+        or a Series.
+
+        Assumes that `series.index is self`
+        """
+        new_values = series._values[loc]
+        if is_scalar(loc):
+            return new_values
+
+        new_index = self[loc]
+        new_index = maybe_droplevels(new_index, key)
+        new_ser = series._constructor(new_values, index=new_index, name=series.name)
+        return new_ser.__finalize__(series)
+
     def _convert_listlike_indexer(self, keyarr):
         """
         Parameters