ENH: implement ExtensionIndex.insert (pandas-dev#32476)

pandas/core/indexes/base.py

@@ -5195,9 +5195,11 @@ def insert(self, loc: int, item):
         -------
         new_index : Index
         """
-        _self = np.asarray(self)
-        item = self._coerce_scalar_to_index(item)._ndarray_values
-        idx = np.concatenate((_self[:loc], item, _self[loc:]))
+        # Note: this method is overriden by all ExtensionIndex subclasses,
+        #  so self is never backed by an EA.
+        arr = np.asarray(self)
+        item = self._coerce_scalar_to_index(item)._values
+        idx = np.concatenate((arr[:loc], item, arr[loc:]))
         return self._shallow_copy_with_infer(idx)
 
     def drop(self, labels, errors: str_t = "raise"):

pandas/core/indexes/extension.py

@@ -6,6 +6,7 @@
 import numpy as np
 
 from pandas.compat.numpy import function as nv
+from pandas.errors import AbstractMethodError
 from pandas.util._decorators import Appender, cache_readonly
 
 from pandas.core.dtypes.common import (
@@ -248,6 +249,10 @@ def repeat(self, repeats, axis=None):
         result = self._data.repeat(repeats, axis=axis)
         return self._shallow_copy(result)
 
+    def insert(self, loc: int, item):
+        # ExtensionIndex subclasses must override Index.insert
+        raise AbstractMethodError(self)
+
     def _concat_same_dtype(self, to_concat, name):
         arr = type(self._data)._concat_same_type(to_concat)
         return type(self)._simple_new(arr, name=name)