BUG: Fix promote_types float32->m8 behavior

numpy · Jun 19, 2020 · 18f2008 · 18f2008
1 parent f253a7e
commit 18f2008
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Showing 3 changed files with 12 additions and 2 deletions.
diff --git a/doc/release/upcoming_changes/16592.compatibility.rst b/doc/release/upcoming_changes/16592.compatibility.rst
@@ -0,0 +1,7 @@
+float->timedelta promotion will raise a TypeError
+-------------------------------------------------
+Float and timedelta promotion consistently raises a TypeError.
+``np.promote_types("float32", "m8")`` aligns with
+``np.promote_types("m8", "float32")`` now and both raise a TypeError.
+Previously, ``np.promote_types("float32", "m8")`` returned ``"m8"`` which
+was considered a bug.
diff --git a/numpy/core/src/multiarray/convert_datatype.c b/numpy/core/src/multiarray/convert_datatype.c
@@ -1419,8 +1419,7 @@ PyArray_PromoteTypes(PyArray_Descr *type1, PyArray_Descr *type2)
             }
             break;
         case NPY_TIMEDELTA:
-            if (PyTypeNum_ISINTEGER(type_num1) ||
-                            PyTypeNum_ISFLOAT(type_num1)) {
+            if (PyTypeNum_ISINTEGER(type_num1)) {
                 return ensure_dtype_nbo(type2);
             }
             break;

diff --git a/numpy/core/tests/test_datetime.py b/numpy/core/tests/test_datetime.py
@@ -775,6 +775,10 @@ def test_dtype_promotion(self):
                             np.dtype('m8[Y]'), np.dtype('m8[D]'))
         assert_raises(TypeError, np.promote_types,
                             np.dtype('m8[M]'), np.dtype('m8[W]'))
+        # timedelta and float cannot be safely cast with each other
+        assert_raises(TypeError, np.promote_types, "float32", "m8")
+        assert_raises(TypeError, np.promote_types, "m8", "float32")
+
         # timedelta <op> timedelta may overflow with big unit ranges
         assert_raises(OverflowError, np.promote_types,
                             np.dtype('m8[W]'), np.dtype('m8[fs]'))