Make validate use best_match.

This function is essentially meant to be the
'dead simple', newbie friendly entry into validation.

Making it use best_match means even friendlier initial
errors, so we switch to using that.

Users who care about potential small effects this has
on performance should already likely be using
an explicitly constructed validator class, and choosing
themselves whether to call best_match or not.

Closes: #498

jsonschema/tests/test_validators.py

@@ -358,13 +358,12 @@ def test_multiple_type_failure(self):
     def test_object_without_title_type_failure(self):
         type = {u"type": [{u"minimum": 3}]}
         message = self.message_for(instance=1, schema={u"type": [type]})
-        self.assertEqual(message, "1 is not of type %r" % (type,))
+        self.assertEqual(message, "1 is less than the minimum of 3")
 
-    def test_object_with_name_type_failure(self):
-        name = "Foo"
-        schema = {u"type": [{u"name": name, u"minimum": 3}]}
+    def test_object_with_named_type_failure(self):
+        schema = {u"type": [{u"name": "Foo", u"minimum": 3}]}
         message = self.message_for(instance=1, schema=schema)
-        self.assertEqual(message, "1 is not of type %r" % (name,))
+        self.assertEqual(message, "1 is less than the minimum of 3")
 
     def test_minimum(self):
         message = self.message_for(instance=1, schema={"minimum": 2})
@@ -1324,6 +1323,13 @@ def test_schema_error_message(self):
             "(?s)Failed validating u?'.*' in metaschema.*On schema",
         )
 
+    def test_it_uses_best_match(self):
+        # This is a schema that best_match will recurse into
+        schema = {"oneOf": [{"type": "string"}, {"type": "array"}]}
+        with self.assertRaises(exceptions.ValidationError) as e:
+            validators.validate(12, schema)
+        self.assertIn("12 is not of type", str(e.exception))
+
 
 class TestRefResolver(SynchronousTestCase):
 

jsonschema/validators.py

@@ -862,8 +862,12 @@ def validate(instance, schema, cls=None, *args, **kwargs):
     """
     if cls is None:
         cls = validator_for(schema)
+
     cls.check_schema(schema)
-    cls(schema, *args, **kwargs).validate(instance)
+    validator = cls(schema, *args, **kwargs)
+    error = exceptions.best_match(validator.iter_errors(instance))
+    if error is not None:
+        raise error
 
 
 def validator_for(schema, default=_LATEST_VERSION):