BUG: Fix Series.get() for ExtensionArray and Categorical (#20885)

Author: Dr-Irv

pandas/core/indexes/base.py

@@ -3082,12 +3082,17 @@ def get_value(self, series, key):
         # use this, e.g. DatetimeIndex
         s = getattr(series, '_values', None)
         if isinstance(s, (ExtensionArray, Index)) and is_scalar(key):
+            # GH 20825
+            # Unify Index and ExtensionArray treatment
+            # First try to convert the key to a location
+            # If that fails, see if key is an integer, and
+            # try that
             try:
-                return s[key]
-            except (IndexError, ValueError):
-
-                # invalid type as an indexer
-                pass
+                iloc = self.get_loc(key)
+                return s[iloc]
+            except KeyError:
+                if is_integer(key):
+                    return s[key]
 
         s = com._values_from_object(series)
         k = com._values_from_object(key)

pandas/tests/extension/base/getitem.py

@@ -117,6 +117,36 @@ def test_getitem_slice(self, data):
         result = data[slice(1)]  # scalar
         assert isinstance(result, type(data))
 
+    def test_get(self, data):
+        # GH 20882
+        s = pd.Series(data, index=[2 * i for i in range(len(data))])
+        assert s.get(4) == s.iloc[2]
+
+        result = s.get([4, 6])
+        expected = s.iloc[[2, 3]]
+        self.assert_series_equal(result, expected)
+
+        result = s.get(slice(2))
+        expected = s.iloc[[0, 1]]
+        self.assert_series_equal(result, expected)
+
+        assert s.get(-1) == s.iloc[-1]
+        assert s.get(s.index.max() + 1) is None
+
+        s = pd.Series(data[:6], index=list('abcdef'))
+        assert s.get('c') == s.iloc[2]
+
+        result = s.get(slice('b', 'd'))
+        expected = s.iloc[[1, 2, 3]]
+        self.assert_series_equal(result, expected)
+
+        result = s.get('Z')
+        assert result is None
+
+        assert s.get(4) == s.iloc[4]
+        assert s.get(-1) == s.iloc[-1]
+        assert s.get(len(s)) is None
+
     def test_take_sequence(self, data):
         result = pd.Series(data)[[0, 1, 3]]
         assert result.iloc[0] == data[0]