Index: Lib/csv.py
===================================================================
--- Lib/csv.py	(revision 69989)
+++ Lib/csv.py	(working copy)
@@ -202,11 +202,15 @@
         """
 
         matches = []
+        if isinstance(data, bytes):
+            b = bytes
+        else:
+            b = lambda x,y: x
         for restr in ('(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)', # ,".*?",
                       '(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?P<delim>[^\w\n"\'])(?P<space> ?)',   #  ".*?",
                       '(?P<delim>>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?:$|\n)',  # ,".*?"
                       '(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?:$|\n)'):                            #  ".*?" (no delim, no space)
-            regexp = re.compile(restr, re.DOTALL | re.MULTILINE)
+            regexp = re.compile(b(restr, "ascii"), re.DOTALL | re.MULTILINE)
             matches = regexp.findall(data)
             if matches:
                 break
@@ -270,8 +274,10 @@
         additional chunks as necessary.
         """
 
-        data = list(filter(None, data.split('\n')))
-
+        if isinstance(data, bytes):
+            data = [s for s in data.split(b"\n") if s]
+        else:
+            data = [s for s in data.split("\n") if s]
         ascii = [chr(c) for c in range(127)] # 7-bit ASCII
 
         # build frequency tables
Index: Lib/test/test_csv.py
===================================================================
--- Lib/test/test_csv.py	(revision 69989)
+++ Lib/test/test_csv.py	(working copy)
@@ -813,6 +813,16 @@
         self.assertEqual(dialect.delimiter, "|")
         self.assertEqual(dialect.quotechar, "'")
 
+    def test_issue5322(self):
+        sniffer = csv.Sniffer()
+        sample = bytes(self.sample3, "ascii")
+        dialect = sniffer.sniff(sample)
+        self.assert_(bytes(dialect.delimiter) in sample)
+        dialect = sniffer.sniff(sample, delimiters="?,")
+        self.assertEqual(dialect.delimiter, "?")
+        dialect = sniffer.sniff(sample, delimiters="/,")
+        self.assertEqual(dialect.delimiter, "/")
+
 if not hasattr(sys, "gettotalrefcount"):
     if support.verbose: print("*** skipping leakage tests ***")
 else: