bpo-32255: Always quote a single empty field when write into a CSV file. (GH-4769) (#4810)

This allows to distinguish an empty row from a row consisting of a single empty field.
(cherry picked from commit 2001900b0c02a397d8cf1d776a7cc7fcb2a463e3)

1 files changed, 20 insertions, 1 deletions

diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 03ab184..fe24801 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -207,10 +207,29 @@ class Test_Csv(unittest.TestCase):
         with TemporaryFile("w+", newline='') as fileobj:
             writer = csv.writer(fileobj)
             self.assertRaises(TypeError, writer.writerows, None)
-            writer.writerows([['a','b'],['c','d']])
+            writer.writerows([['a', 'b'], ['c', 'd']])
             fileobj.seek(0)
             self.assertEqual(fileobj.read(), "a,b\r\nc,d\r\n")
 
+    def test_writerows_with_none(self):
+        with TemporaryFile("w+", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([['a', None], [None, 'd']])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), "a,\r\n,d\r\n")
+
+        with TemporaryFile("w+", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([[None], ['a']])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), '""\r\na\r\n')
+
+        with TemporaryFile("w+", newline='') as fileobj:
+            writer = csv.writer(fileobj)
+            writer.writerows([['a'], [None]])
+            fileobj.seek(0)
+            self.assertEqual(fileobj.read(), 'a\r\n""\r\n')
+
     @support.cpython_only
     def test_writerows_legacy_strings(self):
         import _testcapi