Merge pull request #17161 from seberg/user_type_safe_casting

BUG: Remove Void special case for "safe casting"

2 files changed, 25 insertions, 19 deletions

diff --git a/numpy/core/src/multiarray/convert_datatype.c b/numpy/core/src/multiarray/convert_datatype.c
index 1f5845eb7..d9121707b 100644
--- a/numpy/core/src/multiarray/convert_datatype.c
+++ b/numpy/core/src/multiarray/convert_datatype.c
@@ -343,25 +343,6 @@ PyArray_CanCastSafely(int fromtype, int totype)
     if (fromtype == totype) {
         return 1;
     }
-    /* Special-cases for some types */
-    switch (fromtype) {
-        case NPY_DATETIME:
-        case NPY_TIMEDELTA:
-        case NPY_OBJECT:
-        case NPY_VOID:
-            return 0;
-        case NPY_BOOL:
-            return 1;
-    }
-    switch (totype) {
-        case NPY_BOOL:
-        case NPY_DATETIME:
-        case NPY_TIMEDELTA:
-            return 0;
-        case NPY_OBJECT:
-        case NPY_VOID:
-            return 1;
-    }
 
     from = PyArray_DescrFromType(fromtype);
     /*
diff --git a/numpy/core/tests/test_numeric.py b/numpy/core/tests/test_numeric.py
index badf48b33..0b27c54dd 100644
--- a/numpy/core/tests/test_numeric.py
+++ b/numpy/core/tests/test_numeric.py
@@ -14,6 +14,7 @@ from numpy.testing import (
     assert_array_equal, assert_almost_equal, assert_array_almost_equal,
     assert_warns, assert_array_max_ulp, HAS_REFCOUNT
     )
+from numpy.core._rational_tests import rational
 
 from hypothesis import assume, given, strategies as st
 from hypothesis.extra import numpy as hynp
@@ -863,6 +864,30 @@ class TestTypes:
         assert_equal(np.promote_types('<m8', '<m8'), np.dtype('m8'))
         assert_equal(np.promote_types('>m8', '>m8'), np.dtype('m8'))
 
+    def test_can_cast_and_promote_usertypes(self):
+        # The rational type defines safe casting for signed integers,
+        # boolean. Rational itself *does* cast safely to double.
+        # (rational does not actually cast to all signed integers, e.g.
+        # int64 can be both long and longlong and it registers only the first)
+        valid_types = ["int8", "int16", "int32", "int64", "bool"]
+        invalid_types = "BHILQP" + "FDG" + "mM" + "f" + "V"
+
+        rational_dt = np.dtype(rational)
+        for numpy_dtype in valid_types:
+            numpy_dtype = np.dtype(numpy_dtype)
+            assert np.can_cast(numpy_dtype, rational_dt)
+            assert np.promote_types(numpy_dtype, rational_dt) is rational_dt
+
+        for numpy_dtype in invalid_types:
+            numpy_dtype = np.dtype(numpy_dtype)
+            assert not np.can_cast(numpy_dtype, rational_dt)
+            with pytest.raises(TypeError):
+                np.promote_types(numpy_dtype, rational_dt)
+
+        double_dt = np.dtype("double")
+        assert np.can_cast(rational_dt, double_dt)
+        assert np.promote_types(double_dt, rational_dt) is double_dt
+
     def test_promote_types_strings(self):
         assert_equal(np.promote_types('bool', 'S'), np.dtype('S5'))
         assert_equal(np.promote_types('b', 'S'), np.dtype('S4'))