Fix printing object reference on StringType

<object>.pattern is the correct pattern string from which the object
was compiled from.

Change-Id: I35eeca17d6edcc1a210ed7b3de2856a678fdc180
Closes-Bug: #1340879

wsme/tests/test_types.py

@@ -326,6 +326,15 @@ Value: 'v3'. Value should be one of: v., v.",
         v.validate('A')
         self.assertRaises(ValueError, v.validate, '_')
 
+    def test_validate_string_type_pattern_exception_message(self):
+        regex = '^[a-zA-Z0-9]*$'
+        v = types.StringType(pattern=regex)
+        try:
+            v.validate('_')
+            self.assertFail()
+        except ValueError as e:
+            self.assertIn(regex, str(e))
+
     def test_validate_ipv4_address_type(self):
         v = types.IPv4AddressType()
         v.validate('127.0.0.1')

wsme/types.py

@@ -218,7 +218,7 @@ class StringType(UserType):
             raise ValueError(error)
 
         if self.pattern is not None and not self.pattern.search(value):
-            error = 'Value should match the pattern %s' % self.pattern
+            error = 'Value should match the pattern %s' % self.pattern.pattern
             raise ValueError(error)
 
         return value