Re-word whatsnew entry; use compat.PY3

doc/source/whatsnew/v0.21.0.txt

@@ -127,7 +127,7 @@ Sparse
 Reshaping
 ^^^^^^^^^
 
-- `{arg,idx}{min,max}` on Series, DataFrame, and GroupBy objects work correctly with float data that contains infinite values (:issue:`13595`), and with string data as long as it does not have any missing values.
+- `argmin`, `argmax`, `idxmin`, and `idxmax` on Series, DataFrame, and GroupBy objects work correctly with floating point data that contains infinite values (:issue:`13595`). These functions now also work with string data, as long as there are no missing values.
 
 Numeric
 ^^^^^^^

pandas/tests/series/test_operators.py

@@ -21,7 +21,7 @@
 from pandas.core.indexes.timedeltas import Timedelta
 import pandas.core.nanops as nanops
 
-from pandas.compat import range, zip
+from pandas.compat import range, zip, PY3
 from pandas import compat
 from pandas.util.testing import (assert_series_equal, assert_almost_equal,
                                  assert_frame_equal, assert_index_equal)
@@ -1910,12 +1910,7 @@ def test_argminmax(self):
         # and raise a TypeError.
         s = pd.Series(['foo', 'foo', 'bar', 'bar', None, np.nan, 'baz'])
 
-        if sys.version_info[0] < 3:
-            assert s.argmin() == 4
-            assert np.isnan(s.argmin(skipna=False))
-            assert s.argmax() == 0
-            assert np.isnan(s.argmax(skipna=False))
-        else:
+        if PY3:
             with pytest.raises(TypeError):
                 s.argmin()
             with pytest.raises(TypeError):
@@ -1924,3 +1919,8 @@ def test_argminmax(self):
                 s.argmax()
             with pytest.raises(TypeError):
                 s.argmax(skipna=False)
+        else:
+            assert s.argmin() == 4
+            assert np.isnan(s.argmin(skipna=False))
+            assert s.argmax() == 0
+            assert np.isnan(s.argmax(skipna=False))