REF: Defer creating Index._engine until needed (#58370)

Author: mroeschke

pandas/core/frame.py

@@ -4012,7 +4012,6 @@ def _get_value(self, index, col, takeable: bool = False) -> Scalar:
             return series._values[index]
 
         series = self._get_item(col)
-        engine = self.index._engine
 
         if not isinstance(self.index, MultiIndex):
             # CategoricalIndex: Trying to use the engine fastpath may give incorrect
@@ -4023,7 +4022,7 @@ def _get_value(self, index, col, takeable: bool = False) -> Scalar:
 
         # For MultiIndex going through engine effectively restricts us to
         #  same-length tuples; see test_get_set_value_no_partial_indexing
-        loc = engine.get_loc(index)
+        loc = self.index._engine.get_loc(index)
         return series._values[loc]
 
     def isetitem(self, loc, value) -> None:

pandas/core/indexes/base.py

@@ -832,7 +832,8 @@ def _reset_identity(self) -> None:
 
     @final
     def _cleanup(self) -> None:
-        self._engine.clear_mapping()
+        if "_engine" in self._cache:
+            self._engine.clear_mapping()
 
     @cache_readonly
     def _engine(