BUG: Avoid TypeError in numpy.issubdtype when uninterpretable input type

riku-sakamoto · riku-sakamoto · commit db6a3008b55f · 2025-07-26T22:24:47.000+09:00
As reported in #28946, `numpy.issubdtype` raises TypeError when given uninterpretable type. This commit adds try-except guard to handle such cases.
diff --git a/numpy/_core/numerictypes.py b/numpy/_core/numerictypes.py
@@ -530,10 +530,15 @@ def issubdtype(arg1, arg2):
     True
 
     """
-    if not issubclass_(arg1, generic):
-        arg1 = dtype(arg1).type
-    if not issubclass_(arg2, generic):
-        arg2 = dtype(arg2).type
+    try:
+        if not issubclass_(arg1, generic):
+            arg1 = dtype(arg1).type
+        if not issubclass_(arg2, generic):
+            arg2 = dtype(arg2).type
+    except TypeError:
+        # If either arg1 or arg2 cannot be casted to dtype object,
+        # they are not subdtype. (See #-28946)
+        return False
 
     return issubclass(arg1, arg2)
 
diff --git a/numpy/_core/tests/test_numerictypes.py b/numpy/_core/tests/test_numerictypes.py
@@ -3,6 +3,7 @@
 
 import pytest
 
+from typing import Union
 import numpy as np
 import numpy._core.numerictypes as nt
 from numpy._core.numerictypes import issctype, maximum_sctype, sctype2char, sctypes
@@ -407,6 +408,10 @@ def test_nondtype_nonscalartype(self):
         assert not np.issubdtype(np.float32, "float")
         assert not np.issubdtype(np.float64, "f")
 
+        # Some type cannot be interpreted by numpy
+        assert not np.issubdtype(Union[str, int], np.number)
+        assert not np.issubdtype(np.number, Union[str, int, float])
+
         # Test the same for the correct first datatype and abstract one
         # in the case of int, float, complex:
         assert np.issubdtype(np.float64, 'float64')
