fail on float16, but allow np.exp(int8_arrays)

Author: Terji Petersen

pandas/core/indexes/base.py

@@ -882,6 +882,9 @@ def __array_ufunc__(self, ufunc: np.ufunc, method: str_t, *inputs, **kwargs):
             # i.e. np.divmod, np.modf, np.frexp
             return tuple(self.__array_wrap__(x) for x in result)
 
+        if result.dtype == np.float16:
+            result = result.astype(np.float32)
+
         return self.__array_wrap__(result)
 
     def __array_wrap__(self, result, context=None):

pandas/core/indexes/numeric.py

@@ -134,6 +134,10 @@ def _ensure_array(cls, data, dtype, copy: bool):
         Ensure we have a valid array to pass to _simple_new.
         """
         cls._validate_dtype(dtype)
+        if dtype == np.float16:
+
+            # float16 not supported (no indexing engine)
+            raise NotImplementedError("float16 indexes are not supported")
 
         if not isinstance(data, (np.ndarray, Index)):
             # Coerce to ndarray if not already ndarray or Index

pandas/tests/indexes/numeric/test_numeric.py

@@ -474,11 +474,39 @@ def test_coerce_list(self):
 class TestFloat16Index:
     # float 16 indexes not supported
     # GH 49535
-    def test_array(self):
-        arr = np.array([1, 2, 3], dtype=np.float16)
-        msg = "float16 indexes are not implemented"
+    _index_cls = NumericIndex
+
+    def test_constructor(self):
+        index_cls = self._index_cls
+        dtype = np.float16
+
+        msg = "float16 indexes are not supported"
+
+        # explicit construction
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls([1, 2, 3, 4, 5], dtype=dtype)
+
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls(np.array([1, 2, 3, 4, 5]), dtype=dtype)
+
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls([1.0, 2, 3, 4, 5], dtype=dtype)
+
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls(np.array([1.0, 2, 3, 4, 5]), dtype=dtype)
+
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls([1.0, 2, 3, 4, 5], dtype=dtype)
+
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls(np.array([1.0, 2, 3, 4, 5]), dtype=dtype)
+
+        # nan handling
+        with pytest.raises(NotImplementedError, match=msg):
+            index_cls([np.nan, np.nan], dtype=dtype)
+
         with pytest.raises(NotImplementedError, match=msg):
-            NumericIndex(arr)
+            index_cls(np.array([np.nan]), dtype=dtype)
 
 
 class TestUIntNumericIndex(NumericInt):

pandas/tests/indexes/test_numpy_compat.py

@@ -77,7 +77,10 @@ def test_numpy_ufuncs_basic(index, func):
         # coerces to float (e.g. np.sin)
         with np.errstate(all="ignore"):
             result = func(index)
-            exp = Index(func(index.values), name=index.name)
+            arr_result = func(index.values)
+            if arr_result.dtype == np.float16:
+                arr_result = arr_result.astype(np.float32)
+            exp = Index(arr_result, name=index.name)
 
         tm.assert_index_equal(result, exp)
         if type(index) is not Index or index.dtype == bool: