FIX isfileobj accepts write-mode files under PY3

2 files changed, 20 insertions, 1 deletions

diff --git a/numpy/compat/py3k.py b/numpy/compat/py3k.py
index f5ac3f9f8..4607d9502 100644
--- a/numpy/compat/py3k.py
+++ b/numpy/compat/py3k.py
@@ -36,7 +36,7 @@ if sys.version_info[0] >= 3:
         return str(s)
 
     def isfileobj(f):
-        return isinstance(f, (io.FileIO, io.BufferedReader))
+        return isinstance(f, (io.FileIO, io.BufferedReader, io.BufferedWriter))
 
     def open_latin1(filename, mode='r'):
         return open(filename, mode=mode, encoding='iso-8859-1')
diff --git a/numpy/compat/tests/test_compat.py b/numpy/compat/tests/test_compat.py
new file mode 100644
index 000000000..3df142e04
--- /dev/null
+++ b/numpy/compat/tests/test_compat.py
@@ -0,0 +1,19 @@
+from os.path import join
+
+from numpy.compat import isfileobj
+from numpy.testing import TestCase, assert_
+from numpy.testing.utils import tempdir
+
+
+def test_isfileobj():
+    with tempdir(prefix="numpy_test_compat_") as folder:
+        filename = join(folder, 'a.bin')
+
+        with open(filename, 'wb') as f:
+            assert_(isfileobj(f))
+
+        with open(filename, 'ab') as f:
+            assert_(isfileobj(f))
+
+        with open(filename, 'rb') as f:
+            assert_(isfileobj(f))