bpo-27497: Add return value to csv.DictWriter.writeheader (GH-12306)

csv.DictWriter.writeheader() now returns the return value of the
underlying csv.Writer.writerow() method.

Patch contributed by Ashish Nitin Patil.

2 files changed, 7 insertions, 1 deletions

diff --git a/Lib/csv.py b/Lib/csv.py
index eeeedab..dc85077 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -140,7 +140,7 @@ class DictWriter:
 
     def writeheader(self):
         header = dict(zip(self.fieldnames, self.fieldnames))
-        self.writerow(header)
+        return self.writerow(header)
 
     def _dict_to_list(self, rowdict):
         if self.extrasaction == "raise":
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 7a33313..a16d140 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -608,6 +608,12 @@ class TestQuotedEscapedExcel(TestCsvBase):
 class TestDictFields(unittest.TestCase):
     ### "long" means the row is longer than the number of fieldnames
     ### "short" means there are fewer elements in the row than fieldnames
+    def test_writeheader_return_value(self):
+        with TemporaryFile("w+", newline='') as fileobj:
+            writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
+            writeheader_return_value = writer.writeheader()
+            self.assertEqual(writeheader_return_value, 10)
+
     def test_write_simple_dict(self):
         with TemporaryFile("w+", newline='') as fileobj:
             writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])