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

1 files changed, 2 insertions, 1 deletions

diff --git a/Lib/csv.py b/Lib/csv.py
index 309a8f3..4ef8be4 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -139,7 +139,8 @@ class DictWriter:
             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