fix formatting of GTIDs under py3 (#227)

Author: Roguelazer

pymysqlreplication/event.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import binascii
 import struct
 import datetime
 
@@ -63,9 +64,10 @@ def gtid(self):
         """GTID = source_id:transaction_id
         Eg: 3E11FA47-71CA-11E1-9E33-C80AA9429562:23
         See: http://dev.mysql.com/doc/refman/5.6/en/replication-gtids-concepts.html"""
-        gtid = "%s%s%s%s-%s%s-%s%s-%s%s-%s%s%s%s%s%s" %\
-               tuple("{0:02x}".format(ord(c)) for c in self.sid)
-        gtid += ":%d" % self.gno
+        nibbles = binascii.hexlify(self.sid).decode('ascii')
+        gtid = '%s-%s-%s-%s:%d' % (
+            nibbles[:8], nibbles[8:12], nibbles[12:16], nibbles[16:], self.gno
+        )
         return gtid
 
     def _dump(self):