bpo-1613500: Don't hardcode output file mode in fileinput.FileInput (GH-12986)

1 files changed, 10 insertions, 0 deletions

diff --git a/Lib/test/test_fileinput.py b/Lib/test/test_fileinput.py
index 3857401ca6..8b7577b020 100644
--- a/Lib/test/test_fileinput.py
+++ b/Lib/test/test_fileinput.py
@@ -329,6 +329,16 @@ class FileInputTests(BaseTests, unittest.TestCase):
             self.assertEqual(fi.readline(), b'')
             self.assertEqual(fi.readline(), b'')
 
+    def test_inplace_binary_write_mode(self):
+        temp_file = self.writeTmp(b'Initial text.', mode='wb')
+        with FileInput(temp_file, mode='rb', inplace=True) as fobj:
+            line = fobj.readline()
+            self.assertEqual(line, b'Initial text.')
+            # print() cannot be used with files opened in binary mode.
+            sys.stdout.write(b'New line.')
+        with open(temp_file, 'rb') as f:
+            self.assertEqual(f.read(), b'New line.')
+
     def test_context_manager(self):
         t1 = self.writeTmp("A\nB\nC")
         t2 = self.writeTmp("D\nE\nF")