From 94fe3f58d07f1ae5e9ffb10f149498b09aa12a25 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Tue, 13 Mar 2007 09:32:11 +0000
Subject: [PATCH] Patch #1635454: the csv.DictWriter class now includes the
 offending field names in its exception message if you try to write a record
 with a dictionary containing fields not in the CSV field names list.

---
 Lib/csv.py | 7 ++++---
 Misc/NEWS  | 4 ++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/Lib/csv.py b/Lib/csv.py
index f213854783e..8c6b7401271 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -115,9 +115,10 @@ class DictWriter:
 
     def _dict_to_list(self, rowdict):
         if self.extrasaction == "raise":
-            for k in rowdict.keys():
-                if k not in self.fieldnames:
-                    raise ValueError, "dict contains fields not in fieldnames"
+            wrong_fields = [k for k in rowdict if k not in self.fieldnames]
+            if wrong_fields:
+                raise ValueError("dict contains fields not in fieldnames: " +
+                                 ", ".join(wrong_fields))
         return [rowdict.get(key, self.restval) for key in self.fieldnames]
 
     def writerow(self, rowdict):
diff --git a/Misc/NEWS b/Misc/NEWS
index 79d242b03a7..33f6d9a09c3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -168,6 +168,10 @@ Core and builtins
 Library
 -------
 
+- Patch #1635454: the csv.DictWriter class now includes the offending
+  field names in its exception message if you try to write a record with
+  a dictionary containing fields not in the CSV field names list.
+
 - Patch #1668100: urllib2 now correctly raises URLError instead of
   OSError if accessing a local file via the file:// protocol fails.