clean up blueprint json support

add changelog for #1898

CHANGES

@@ -27,8 +27,11 @@ Major release, unreleased
 - ``MethodView`` can inherit method handlers from base classes. (`#1936`_)
 - Errors caused while opening the session at the beginning of the request are
   handled by the app's error handlers. (`#2254`_)
+- Blueprints gained ``json_encoder`` and ``json_decoder`` attributes to
+  override the app's encoder and decoder. (`#1898`_)
 
 .. _#1489: https://github.com/pallets/flask/pull/1489
+.. _#1898: https://github.com/pallets/flask/pull/1898
 .. _#1936: https://github.com/pallets/flask/pull/1936
 .. _#2017: https://github.com/pallets/flask/pull/2017
 .. _#2223: https://github.com/pallets/flask/pull/2223

flask/blueprints.py

@@ -90,10 +90,10 @@ class Blueprint(_PackageBoundObject):
     _got_registered_once = False
 
     #: Blueprint local JSON decoder class to use.
-    # Set to None to use the :class:`~flask.app.Flask.json_encoder`.
+    #: Set to ``None`` to use the app's :class:`~flask.app.Flask.json_encoder`.
     json_encoder = None
     #: Blueprint local JSON decoder class to use.
-    # Set to None to use the :class:`~flask.app.Flask.json_decoder`.
+    #: Set to ``None`` to use the app's :class:`~flask.app.Flask.json_decoder`.
     json_decoder = None
 
     def __init__(self, name, import_name, static_folder=None,

flask/json.py

@@ -92,13 +92,16 @@ class JSONDecoder(_json.JSONDecoder):
 def _dump_arg_defaults(kwargs):
     """Inject default arguments for dump functions."""
     if current_app:
-        bp = current_app.blueprints.get(request.blueprint,
+        bp = current_app.blueprints.get(request.blueprint) if request else None
-                                        None) if has_request_context() else None
+        kwargs.setdefault(
-        kwargs.setdefault('cls',
+            'cls',
-                          bp.json_encoder if bp and bp.json_encoder
+            bp.json_encoder if bp and bp.json_encoder
-                          else current_app.json_encoder)
+                else current_app.json_encoder
+        )
+
         if not current_app.config['JSON_AS_ASCII']:
             kwargs.setdefault('ensure_ascii', False)
+
         kwargs.setdefault('sort_keys', current_app.config['JSON_SORT_KEYS'])
     else:
         kwargs.setdefault('sort_keys', True)
@@ -108,11 +111,12 @@ def _dump_arg_defaults(kwargs):
 def _load_arg_defaults(kwargs):
     """Inject default arguments for load functions."""
     if current_app:
-        bp = current_app.blueprints.get(request.blueprint,
+        bp = current_app.blueprints.get(request.blueprint) if request else None
-                                        None) if has_request_context() else None
+        kwargs.setdefault(
-        kwargs.setdefault('cls',
+            'cls',
-                          bp.json_decoder if bp and bp.json_decoder
+            bp.json_decoder if bp and bp.json_decoder
-                          else current_app.json_decoder)
+                else current_app.json_decoder
+        )
     else:
         kwargs.setdefault('cls', JSONDecoder)
 

tests/test_helpers.py

@@ -271,30 +271,36 @@ class TestJSON(object):
         class X(object):
             def __init__(self, val):
                 self.val = val
+
         class MyEncoder(flask.json.JSONEncoder):
             def default(self, o):
                 if isinstance(o, X):
                     return '<%d>' % o.val
+
                 return flask.json.JSONEncoder.default(self, o)
+
         class MyDecoder(flask.json.JSONDecoder):
             def __init__(self, *args, **kwargs):
                 kwargs.setdefault('object_hook', self.object_hook)
                 flask.json.JSONDecoder.__init__(self, *args, **kwargs)
+
             def object_hook(self, obj):
                 if len(obj) == 1 and '_foo' in obj:
                     return X(obj['_foo'])
+
                 return obj
 
-        blue = flask.Blueprint('blue', __name__)
+        bp = flask.Blueprint('bp', __name__)
-        blue.json_encoder = MyEncoder
+        bp.json_encoder = MyEncoder
-        blue.json_decoder = MyDecoder
+        bp.json_decoder = MyDecoder
-        @blue.route('/bp', methods=['POST'])
+
+        @bp.route('/bp', methods=['POST'])
         def index():
             return flask.json.dumps(flask.request.get_json()['x'])
 
         app = flask.Flask(__name__)
         app.testing = True
-        app.register_blueprint(blue)
+        app.register_blueprint(bp)
 
         c = app.test_client()
         rv = c.post('/bp', data=flask.json.dumps({