BUG: fixed index power operation

The power operation on a range of indexes was fixed.
closes #14973

Author: Kamal Kamalaldin <[email protected]>

Closes #14996 from kamal94/master and squashes the following commits:

66c2338 [Kamal Kamalaldin] Merge branch 'master' of git://github.com/pandas-dev/pandas
14c47a8 [Kamal Kamalaldin] DOC: updated wording of a previous fix
a6c9458 [Kamal Kamalaldin] BUG: fixed index power operation

Author: kamal94

doc/source/whatsnew/v0.20.0.txt

@@ -283,6 +283,7 @@ Performance Improvements
 Bug Fixes
 ~~~~~~~~~
 
+- Bug in ``Index`` power operations with reversed operands (:issue:`14973`)
 - Bug in ``TimedeltaIndex`` addition where overflow was being allowed without error (:issue:`14816`)
 - Bug in ``DataFrame`` construction in which unsigned 64-bit integer elements were being converted to objects (:issue:`14881`)
 - Bug in ``astype()`` where ``inf`` values were incorrectly converted to integers. Now raises error now with ``astype()`` for Series and DataFrames (:issue:`14265`)

pandas/indexes/base.py

@@ -3543,7 +3543,9 @@ def _evaluate_numeric_binop(self, other):
             operator.sub, '__sub__', reversed=True)
         cls.__mul__ = cls.__rmul__ = _make_evaluate_binop(
             operator.mul, '__mul__')
-        cls.__pow__ = cls.__rpow__ = _make_evaluate_binop(
+        cls.__rpow__ = _make_evaluate_binop(
+            operator.pow, '__pow__', reversed=True)
+        cls.__pow__ = _make_evaluate_binop(
             operator.pow, '__pow__')
         cls.__mod__ = _make_evaluate_binop(
             operator.mod, '__mod__')

pandas/tests/indexes/test_numeric.py

@@ -105,6 +105,15 @@ def test_numeric_compat(self):
         for r, e in zip(result, expected):
             tm.assert_index_equal(r, e)
 
+        # test power calculations both ways, GH 14973
+        expected = pd.Float64Index(2.0**idx.values)
+        result = 2.0**idx
+        tm.assert_index_equal(result, expected)
+
+        expected = pd.Float64Index(idx.values**2.0)
+        result = idx**2.0
+        tm.assert_index_equal(result, expected)
+
     def test_explicit_conversions(self):
 
         # GH 8608