MNT: implement assert_array_compare without converting array to python list.

1 files changed, 5 insertions, 4 deletions

diff --git a/numpy/testing/_private/utils.py b/numpy/testing/_private/utils.py
index c22348103..3953439f0 100644
--- a/numpy/testing/_private/utils.py
+++ b/numpy/testing/_private/utils.py
@@ -20,7 +20,8 @@ from warnings import WarningMessage
 import pprint
 
 from numpy.core import(
-     float32, empty, arange, array_repr, ndarray, isnat, array)
+     intp, float32, empty, arange, array_repr, ndarray, isnat, array,
+     logical_not)
 from numpy.lib.utils import deprecate
 
 if sys.version_info[0] >= 3:
@@ -784,18 +785,18 @@ def assert_array_compare(comparison, x, y, err_msg='', verbose=True,
 
         if isinstance(val, bool):
             cond = val
-            reduced = [0]
+            reduced = array([0])
         else:
             reduced = val.ravel()
             cond = reduced.all()
-            reduced = reduced.tolist()
 
         # The below comparison is a hack to ensure that fully masked
         # results, for which val.ravel().all() returns np.ma.masked,
         # do not trigger a failure (np.ma.masked != True evaluates as
         # np.ma.masked, which is falsy).
         if cond != True:
-            mismatch = 100.0 * reduced.count(0) / ox.size
+            logical_not(reduced, out=reduced)
+            mismatch = 100.0 * reduced.sum(dtype=intp) / ox.size
             remarks = ['Mismatch: {:.3g}%'.format(mismatch)]
 
             with errstate(invalid='ignore', divide='ignore'):