Add jsonschema.validators.extend

3 files changed, 35 insertions, 2 deletions

diff --git a/docs/creating.rst b/docs/creating.rst
index 1b67011..6467756 100644
--- a/docs/creating.rst
+++ b/docs/creating.rst
@@ -25,6 +25,17 @@ Creating or Extending Validators
         can still have their types customized on a per-instance basis.
     :returns: an :class:`jsonschema.IValidator`
 
+.. autofunction:: extend
+
+    Create a new validator that extends an existing validator.
+
+    :argument :class:`jsonschema.IValidator` validator: an existing validator
+    :argument dict validators: a set of new validators to add to the new
+        validator. Any validators with the same name as an existing one will
+        (silently) replace the old validator entirely.
+    :argument str version: a version for the new validator
+    :returns: an :class:`jsonschema.IValidator`
+
 .. autofunction:: validates
 
 
diff --git a/jsonschema/tests/test_validators.py b/jsonschema/tests/test_validators.py
index 1457be5..5162f6f 100644
--- a/jsonschema/tests/test_validators.py
+++ b/jsonschema/tests/test_validators.py
@@ -9,11 +9,11 @@ from jsonschema.compat import PY3
 from jsonschema.tests.compat import mock, unittest
 from jsonschema.validators import (
     RefResolutionError, UnknownType, ErrorTree, Draft3Validator,
-    Draft4Validator, RefResolver, ValidatorMixin, create, validate,
+    Draft4Validator, RefResolver, ValidatorMixin, create, extend, validate,
 )
 
 
-class TestCreate(unittest.TestCase):
+class TestCreateAndExtend(unittest.TestCase):
     def setUp(self):
         self.meta_schema = {"properties" : {"smelly" : {}}}
         self.smelly = mock.MagicMock()
@@ -63,6 +63,17 @@ class TestCreate(unittest.TestCase):
             create(meta_schema={"id" : "id"})
         self.assertFalse(validates.called)
 
+    def test_extend(self):
+        validators = dict(self.Validator.VALIDATORS)
+        new = mock.Mock()
+
+        Extended = extend(self.Validator, validators={"a new one" : new})
+
+        validators.update([("a new one", new)])
+        self.assertEqual(Extended.VALIDATORS, validators)
+        self.assertEqual(Extended.META_SCHEMA, self.Validator.META_SCHEMA)
+        self.assertEqual(Extended.DEFAULT_TYPES, self.Validator.DEFAULT_TYPES)
+
 
 class TestIterErrors(unittest.TestCase):
     def setUp(self):
diff --git a/jsonschema/validators.py b/jsonschema/validators.py
index 3db7ce9..c8ee8d8 100644
--- a/jsonschema/validators.py
+++ b/jsonschema/validators.py
@@ -146,6 +146,17 @@ def create(meta_schema, validators=(), version=None, default_types=None):  # noq
     return Validator
 
 
+def extend(validator, validators, version=None):
+    all_validators = validator.VALIDATORS
+    all_validators.update(validators)
+    return create(
+        meta_schema=validator.META_SCHEMA,
+        validators=all_validators,
+        version=version,
+        default_types=validator.DEFAULT_TYPES,
+    )
+
+
 class ValidatorMixin(create(meta_schema={})):
     def __init__(self, *args, **kwargs):
         super(ValidatorMixin, self).__init__(*args, **kwargs)