Closes #13761: add a "flush" keyword argument to print().

1 files changed, 26 insertions, 0 deletions

diff --git a/Lib/test/test_print.py b/Lib/test/test_print.py
index 8d37bbc4d6..9d6dbea46b 100644
--- a/Lib/test/test_print.py
+++ b/Lib/test/test_print.py
@@ -111,6 +111,32 @@ class TestPrint(unittest.TestCase):
         self.assertRaises(TypeError, print, '', end=3)
         self.assertRaises(AttributeError, print, '', file='')
 
+    def test_print_flush(self):
+        # operation of the flush flag
+        class filelike():
+            def __init__(self):
+                self.written = ''
+                self.flushed = 0
+            def write(self, str):
+                self.written += str
+            def flush(self):
+                self.flushed += 1
+
+        f = filelike()
+        print(1, file=f, end='', flush=True)
+        print(2, file=f, end='', flush=True)
+        print(3, file=f, flush=False)
+        self.assertEqual(f.written, '123\n')
+        self.assertEqual(f.flushed, 2)
+
+        # ensure exceptions from flush are passed through
+        class noflush():
+            def write(self, str):
+                pass
+            def flush(self):
+                raise RuntimeError
+        self.assertRaises(RuntimeError, print, 1, file=noflush(), flush=True)
+
 def test_main():
     support.run_unittest(TestPrint)