diff -r 6b189f29b1e6 Lib/csv.py
--- a/Lib/csv.py	Wed Jun 05 18:37:50 2013 -0400
+++ b/Lib/csv.py	Sat Jun 08 00:10:36 2013 +0800
@@ -264,8 +264,9 @@
 
         # if we see an extra quote between delimiters, we've got a
         # double quoted format
-        dq_regexp = re.compile(r"((%(delim)s)|^)\W*%(quote)s[^%(delim)s\n]*%(quote)s[^%(delim)s\n]*%(quote)s\W*((%(delim)s)|$)" % \
-                               {'delim':delim, 'quote':quotechar}, re.MULTILINE)
+        dq_regexp = re.compile(
+            r"((%(delim)s)|^)\W*%(quote)s[^%(delim)s\n]*%(quote)s[^%(delim)s\n]*%(quote)s\W*((%(delim)s)|$)" % \
+            {'delim':re.escape(delim), 'quote':quotechar}, re.MULTILINE)
 
 
 
diff -r 6b189f29b1e6 Lib/test/test_csv.py
--- a/Lib/test/test_csv.py	Wed Jun 05 18:37:50 2013 -0400
+++ b/Lib/test/test_csv.py	Sat Jun 08 00:10:36 2013 +0800
@@ -805,7 +805,7 @@
 'Tommy''s Place':'Blue Island':'IL':'12/28/02':'Blue Sunday/White Crow'
 'Stonecutters ''Seafood'' and Chop House':'Lemont':'IL':'12/19/02':'Week Back'
 """
-    header = '''\
+    header1 = '''\
 "venue","city","state","date","performers"
 '''
     sample3 = '''\
@@ -824,10 +824,31 @@
     sample6 = "a|b|c\r\nd|e|f\r\n"
     sample7 = "'a'|'b'|'c'\r\n'd'|e|f\r\n"
 
+    header2 = '''\
+"venue"+"city"+"state"+"date"+"performers"
+'''
+    sample8 = """\
+Harry's+ Arlington Heights+ IL, 2/1/03+ Kimi Hayes
+Shark City+ Glendale Heights+ IL, 12/28/02+ Prezence
+Tommy's Place+ Blue Island+ IL, 12/28/02+ Blue Sunday/White Crow
+Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
+"""
+    sample9 = """\
+Harry''s+ Arlington Heights+ IL, 2/1/03+ Kimi Hayes
+Shark City+ Glendale Heights+ IL, 12/28/02+ Prezence
+Tommy''s Place+ Blue Island+ IL, 12/28/02+ Blue Sunday/White Crow
+Stonecutters ''Seafood'' and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
+"""
+
     def test_has_header(self):
         sniffer = csv.Sniffer()
         self.assertEqual(sniffer.has_header(self.sample1), False)
-        self.assertEqual(sniffer.has_header(self.header+self.sample1), True)
+        self.assertEqual(sniffer.has_header(self.header1 + self.sample1),
+                         True)
+        #test the delimiter which has special meaning in regex (such as +)
+        self.assertEqual(sniffer.has_header(self.sample8), False)
+        self.assertEqual(sniffer.has_header(self.header2 + self.sample8),
+                         True)
 
     def test_sniff(self):
         sniffer = csv.Sniffer()
@@ -864,10 +885,15 @@
 
     def test_doublequote(self):
         sniffer = csv.Sniffer()
-        dialect = sniffer.sniff(self.header)
+        dialect = sniffer.sniff(self.header1)
         self.assertFalse(dialect.doublequote)
         dialect = sniffer.sniff(self.sample2)
         self.assertTrue(dialect.doublequote)
+        #test the delimiter which has special meaning in regex (such as +)
+        dialect = sniffer.sniff(self.sample8)
+        self.assertFalse(dialect.doublequote)
+        dialect = sniffer.sniff(self.sample9)
+        self.assertTrue(dialect.doublequote)
 
 if not hasattr(sys, "gettotalrefcount"):
     if support.verbose: print("*** skipping leakage tests ***")