bpo-44512: Fix handling of extrasactions arg to csv.DictWriter with mixed or upper case (#26924)

Author: akulakov

Lib/csv.py

@@ -139,7 +139,8 @@ def __init__(self, f, fieldnames, restval="", extrasaction="raise",
             fieldnames = list(fieldnames)
         self.fieldnames = fieldnames    # list of keys for the dict
         self.restval = restval          # for writing short dicts
-        if extrasaction.lower() not in ("raise", "ignore"):
+        extrasaction = extrasaction.lower()
+        if extrasaction not in ("raise", "ignore"):
             raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"
                              % extrasaction)
         self.extrasaction = extrasaction

Lib/test/test_csv.py

@@ -762,13 +762,21 @@ def test_write_field_not_in_field_names_raise(self):
         dictrow = {'f0': 0, 'f1': 1, 'f2': 2, 'f3': 3}
         self.assertRaises(ValueError, csv.DictWriter.writerow, writer, dictrow)
 
+        # see bpo-44512 (differently cased 'raise' should not result in 'ignore')
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="RAISE")
+        self.assertRaises(ValueError, csv.DictWriter.writerow, writer, dictrow)
+
     def test_write_field_not_in_field_names_ignore(self):
         fileobj = StringIO()
         writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="ignore")
         dictrow = {'f0': 0, 'f1': 1, 'f2': 2, 'f3': 3}
         csv.DictWriter.writerow(writer, dictrow)
         self.assertEqual(fileobj.getvalue(), "1,2\r\n")
 
+        # bpo-44512
+        writer = csv.DictWriter(fileobj, ['f1', 'f2'], extrasaction="IGNORE")
+        csv.DictWriter.writerow(writer, dictrow)
+
     def test_dict_reader_fieldnames_accepts_iter(self):
         fieldnames = ["a", "b", "c"]
         f = StringIO()

Misc/NEWS.d/next/Library/2022-12-09-10-35-36.bpo-44592.z-P3oe.rst

@@ -0,0 +1,2 @@
+Fixes inconsistent handling of case sensitivity of *extrasaction* arg in
+:class:`csv.DictWriter`.