[3.6] bpo-30157: Fix csv.Sniffer.sniff() regex pattern. (GH-5601) (GH-5603)

Co-authored-by: Jake Davis <jcdavis@awedge.net>.
(cherry picked from commit 2411292ba8155327125d8a1da8a4c9fa003d5909)

2 files changed, 11 insertions, 1 deletions

diff --git a/Lib/csv.py b/Lib/csv.py
index 0349e0b..a05c8da 100644
--- a/Lib/csv.py
+++ b/Lib/csv.py
@@ -217,7 +217,7 @@ class Sniffer:
         matches = []
         for restr in (r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)', # ,".*?",
                       r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?P<delim>[^\w\n"\'])(?P<space> ?)',   #  ".*?",
-                      r'(?P<delim>>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?:$|\n)',  # ,".*?"
+                      r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?:$|\n)',   # ,".*?"
                       r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?:$|\n)'):                            #  ".*?" (no delim, no space)
             regexp = re.compile(restr, re.DOTALL | re.MULTILINE)
             matches = regexp.findall(data)
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index fe24801..b65cbf6 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -986,6 +986,16 @@ Stonecutters Seafood and Chop House+ Lemont+ IL+ 12/19/02+ Week Back
         self.assertEqual(sniffer.has_header(self.header2 + self.sample8),
                          True)
 
+    def test_guess_quote_and_delimiter(self):
+        sniffer = csv.Sniffer()
+        for header in (";'123;4';", "'123;4';", ";'123;4'", "'123;4'"):
+            with self.subTest(header):
+                dialect = sniffer.sniff(header, ",;")
+                self.assertEqual(dialect.delimiter, ';')
+                self.assertEqual(dialect.quotechar, "'")
+                self.assertIs(dialect.doublequote, False)
+                self.assertIs(dialect.skipinitialspace, False)
+
     def test_sniff(self):
         sniffer = csv.Sniffer()
         dialect = sniffer.sniff(self.sample1)