ENH: A more helpful error message, when types don't match type of default kwarg

1 files changed, 14 insertions, 2 deletions

diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index c6db42ce4..ddc919e4f 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -671,11 +671,23 @@ 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:
+        raise TypeError('Choicelist elements do not have a common dtype: {}'
+                        .format(e))
+    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:
+        raise TypeError(
+                'Choicelists and default do not have a common dtype: {}'
+                .format(e))
 
     # Convert conditions to arrays and broadcast conditions and choices
     # as the shape is needed for the result. Doing it separately optimizes