Merge pull request #9089 from shoyer/array-ufunc-error-message

MAINT: refine error message for __array_ufunc__ not implemented

2 files changed, 8 insertions, 7 deletions

diff --git a/numpy/core/_internal.py b/numpy/core/_internal.py
index 10fcbfdfe..9c46b3297 100644
--- a/numpy/core/_internal.py
+++ b/numpy/core/_internal.py
@@ -695,10 +695,11 @@ def array_ufunc_errmsg_formatter(dummy, ufunc, method, *inputs, **kwargs):
                              for k, v in kwargs.items()])
     args = inputs + kwargs.get('out', ())
     types_string = ', '.join(repr(type(arg).__name__) for arg in args)
-    return ('operand type(s) do not implement __array_ufunc__'
-            '({!r}, {!r}, {}): {}'
+    return ('operand type(s) all returned NotImplemented from '
+            '__array_ufunc__({!r}, {!r}, {}): {}'
             .format(ufunc, method, args_string, types_string))
 
+
 def _ufunc_doc_signature_formatter(ufunc):
     """
     Builds a signature string which resembles PEP 457
diff --git a/numpy/core/tests/test_umath.py b/numpy/core/tests/test_umath.py
index 13f29504a..9e849df92 100644
--- a/numpy/core/tests/test_umath.py
+++ b/numpy/core/tests/test_umath.py
@@ -1931,14 +1931,14 @@ class TestSpecialMethods(TestCase):
             def __array_ufunc__(self, *args, **kwargs):
                 return NotImplemented
 
-        msg = ("operand type(s) do not implement __array_ufunc__("
-               "<ufunc 'negative'>, '__call__', <*>): 'A'")
+        msg = ("operand type(s) all returned NotImplemented from "
+               "__array_ufunc__(<ufunc 'negative'>, '__call__', <*>): 'A'")
         with assert_raises_regex(TypeError, fnmatch.translate(msg)):
             np.negative(A())
 
-        msg = ("operand type(s) do not implement __array_ufunc__("
-               "<ufunc 'add'>, '__call__', <*>, <object *>, out=(1,)): "
-               "'A', 'object', 'int'")
+        msg = ("operand type(s) all returned NotImplemented from "
+               "__array_ufunc__(<ufunc 'add'>, '__call__', <*>, <object *>, "
+               "out=(1,)): 'A', 'object', 'int'")
         with assert_raises_regex(TypeError, fnmatch.translate(msg)):
             np.add(A(), object(), out=1)