Merge pull request #18515 from terfilip/select-dtype-err-msg-18430

MAINT: Improve error message when common type not found.

1 files changed, 13 insertions, 2 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index 285f90a6f..af5a6e45c 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -671,11 +671,22 @@ def select(condlist, choicelist, default=0):
         raise ValueError("select with an empty condition list is not possible")
 
     choicelist = [np.asarray(choice) for choice in choicelist]
-    choicelist.append(np.asarray(default))
+
+    try:
+        intermediate_dtype = np.result_type(*choicelist)
+    except TypeError as e:
+        msg = f'Choicelist elements do not have a common dtype: {e}'
+        raise TypeError(msg) from None
+    default_array = np.asarray(default)
+    choicelist.append(default_array)
 
     # need to get the result type before broadcasting for correct scalar
     # behaviour
-    dtype = np.result_type(*choicelist)
+    try:
+        dtype = np.result_type(intermediate_dtype, default_array)
+    except TypeError as e:
+        msg = f'Choicelists and default value do not have a common dtype: {e}'
+        raise TypeError(msg) from None
 
     # Convert conditions to arrays and broadcast conditions and choices
     # as the shape is needed for the result. Doing it separately optimizes