Add priority to decorator processors

marshmallow/decorators.py

@@ -61,15 +61,16 @@ def validate_age(self, data):
 VALIDATES_SCHEMA = 'validates_schema'
 
 
-def validates(field_name):
+def validates(field_name, priority=0):
     """Register a field validator.
 
     :param str field_name: Name of the field that the method validates.
     """
-    return tag_processor(VALIDATES, None, False, field_name=field_name)
+    return tag_processor(VALIDATES, None, False, priority=priority, field_name=field_name)
 
 
-def validates_schema(fn=None, pass_many=False, pass_original=False, skip_on_field_errors=True):
+def validates_schema(fn=None, pass_many=False, pass_original=False, skip_on_field_errors=True,
+                     priority=0):
     """Register a schema-level validator.
 
     By default, receives a single object at a time, regardless of whether ``many=True``
@@ -85,52 +86,52 @@ def validates_schema(fn=None, pass_many=False, pass_original=False, skip_on_fiel
     .. versionchanged:: 3.0.0b1
         ``skip_on_field_errors`` defaults to `True`.
     """
-    return tag_processor(VALIDATES_SCHEMA, fn, pass_many, pass_original=pass_original,
-                         skip_on_field_errors=skip_on_field_errors)
+    return tag_processor(VALIDATES_SCHEMA, fn, pass_many, priority=priority,
+                         pass_original=pass_original, skip_on_field_errors=skip_on_field_errors)
 
 
-def pre_dump(fn=None, pass_many=False):
+def pre_dump(fn=None, pass_many=False, priority=0):
     """Register a method to invoke before serializing an object. The method
     receives the object to be serialized and returns the processed object.
 
     By default, receives a single object at a time, regardless of whether ``many=True``
     is passed to the `Schema`. If ``pass_many=True``, the raw data (which may be a collection)
     and the value for ``many`` is passed.
     """
-    return tag_processor(PRE_DUMP, fn, pass_many)
+    return tag_processor(PRE_DUMP, fn, pass_many, priority=priority)
 
 
-def post_dump(fn=None, pass_many=False, pass_original=False):
+def post_dump(fn=None, pass_many=False, pass_original=False, priority=0):
     """Register a method to invoke after serializing an object. The method
     receives the serialized object and returns the processed object.
 
     By default, receives a single object at a time, transparently handling the ``many``
     argument passed to the Schema. If ``pass_many=True``, the raw data
     (which may be a collection) and the value for ``many`` is passed.
     """
-    return tag_processor(POST_DUMP, fn, pass_many, pass_original=pass_original)
+    return tag_processor(POST_DUMP, fn, pass_many, priority=priority, pass_original=pass_original)
 
 
-def pre_load(fn=None, pass_many=False):
+def pre_load(fn=None, pass_many=False, priority=0):
     """Register a method to invoke before deserializing an object. The method
     receives the data to be deserialized and returns the processed data.
 
     By default, receives a single datum at a time, transparently handling the ``many``
     argument passed to the Schema. If ``pass_many=True``, the raw data
     (which may be a collection) and the value for ``many`` is passed.
     """
-    return tag_processor(PRE_LOAD, fn, pass_many)
+    return tag_processor(PRE_LOAD, fn, pass_many, priority=priority)
 
 
-def post_load(fn=None, pass_many=False, pass_original=False):
+def post_load(fn=None, pass_many=False, pass_original=False, priority=0):
     """Register a method to invoke after deserializing an object. The method
     receives the deserialized data and returns the processed data.
 
     By default, receives a single datum at a time, transparently handling the ``many``
     argument passed to the Schema. If ``pass_many=True``, the raw data
     (which may be a collection) and the value for ``many`` is passed.
     """
-    return tag_processor(POST_LOAD, fn, pass_many, pass_original=pass_original)
+    return tag_processor(POST_LOAD, fn, pass_many, priority=priority, pass_original=pass_original)
 
 
 def tag_processor(tag_name, fn, pass_many, **kwargs):

marshmallow/schema.py

@@ -173,6 +173,16 @@ def _resolve_processors(self):
                 # the processor was a descriptor or something.
                 self.__processors__[tag].append(attr_name)
 
+        # Sort all processor tags by priority, descending
+        for tag, processors in self.__processors__.items():
+            sorted_processors = sorted(processors,
+                                       key=lambda proc: self._get_priority(proc, tag))
+            self.__processors__[tag] = sorted_processors
+
+    def _get_priority(self, attr_name, tag):
+        processor = getattr(self, attr_name)
+        return processor.__marshmallow_kwargs__[tag].get('priority', 0)
+
 
 class SchemaOpts(object):
     """class Meta options for the :class:`Schema`. Defines defaults."""

tests/test_decorators.py

@@ -706,3 +706,29 @@ def raise_value_error(self, item):
         schema.dump(object())
     assert exc.value.messages == {'foo': 'error'}
     schema.load({})
+
+class TestProcessorPriorities:
+
+    def test_pass_ordered_processors(self):
+        class MySchema(Schema):
+            data = fields.Field()
+
+            @post_load(priority=1)
+            def first_post_load(self, ret):
+                ret['data'].append(1)
+                return ret
+
+            @post_load(priority=10)
+            def third_post_load(self, ret):
+                ret['data'].append(10)
+                return ret
+
+            @post_load(priority=5)
+            def second_post_load(self, ret):
+                ret['data'].append(5)
+                return ret
+
+        schema = MySchema()
+        datum = {'data': []}
+        item_loaded = schema.load(datum).data
+        assert item_loaded['data'] == [1, 5, 10]