BUG: Fix Series.get failure on missing NaN (#8569) (#16619)

(cherry picked from commit 2b44868)

doc/source/whatsnew/v0.20.3.txt

@@ -48,7 +48,7 @@ Conversion
 Indexing
 ^^^^^^^^
 
-
+- Bug in ``Float64Index`` causing an empty array instead of None to be returned from ``.get(np.nan)`` on a Series whose index did not contain any NaNs (:issue:`8569`)
 
 I/O
 ^^^

pandas/core/indexes/numeric.py

@@ -369,6 +369,8 @@ def get_loc(self, key, method=None, tolerance=None):
                 except (ValueError, IndexError):
                     # should only need to catch ValueError here but on numpy
                     # 1.7 .item() can raise IndexError when NaNs are present
+                    if not len(nan_idxs):
+                        raise KeyError(key)
                     return nan_idxs
         except (TypeError, NotImplementedError):
             pass

pandas/tests/indexes/test_multi.py

@@ -1172,6 +1172,14 @@ def test_get_loc_level(self):
         assert result == expected
         assert new_index.equals(index.droplevel(0))
 
+    def test_get_loc_missing_nan(self):
+        # GH 8569
+        idx = MultiIndex.from_arrays([[1.0, 2.0], [3.0, 4.0]])
+        assert isinstance(idx.get_loc(1), slice)
+        pytest.raises(KeyError, idx.get_loc, 3)
+        pytest.raises(KeyError, idx.get_loc, np.nan)
+        pytest.raises(KeyError, idx.get_loc, [np.nan])
+
     def test_slice_locs(self):
         df = tm.makeTimeDataFrame()
         stacked = df.stack()

pandas/tests/indexes/test_numeric.py

@@ -371,6 +371,14 @@ def test_get_loc_na(self):
         assert idx.get_loc(1) == 1
         pytest.raises(KeyError, idx.slice_locs, np.nan)
 
+    def test_get_loc_missing_nan(self):
+        # GH 8569
+        idx = Float64Index([1, 2])
+        assert idx.get_loc(1) == 0
+        pytest.raises(KeyError, idx.get_loc, 3)
+        pytest.raises(KeyError, idx.get_loc, np.nan)
+        pytest.raises(KeyError, idx.get_loc, [np.nan])
+
     def test_contains_nans(self):
         i = Float64Index([1.0, 2.0, np.nan])
         assert np.nan in i

pandas/tests/series/test_indexing.py

@@ -70,6 +70,21 @@ def test_get(self):
         result = vc.get(True, default='Missing')
         assert result == 'Missing'
 
+    def test_get_nan(self):
+        # GH 8569
+        s = pd.Float64Index(range(10)).to_series()
+        assert s.get(np.nan) is None
+        assert s.get(np.nan, default='Missing') == 'Missing'
+
+        # ensure that fixing the above hasn't broken get
+        # with multiple elements
+        idx = [20, 30]
+        assert_series_equal(s.get(idx),
+                            Series([np.nan] * 2, index=idx))
+        idx = [np.nan, np.nan]
+        assert_series_equal(s.get(idx),
+                            Series([np.nan] * 2, index=idx))
+
     def test_delitem(self):
 
         # GH 5542