feat: add to export_loop skip_fields arg

schematics/models.py

@@ -173,14 +173,16 @@ class Model(metaclass=ModelMeta):
         return convert(self.__class__, self, raw_data, role=role, **kwargs)
 
     def to_native(self, role=None, app_data=None, **kwargs):
-        data = app_data.get('data')
-        if not data:
+        if app_data and 'data' in app_data:
+            data = app_data['data']
+        else:
             data = self
         return to_native(self.__class__, data, role=role, app_data=app_data, export_level=NOT_NONE, **kwargs)
 
     def to_primitive(self, role=None, app_data=None, **kwargs):
-        data = app_data.get('data')
-        if not data:
+        if app_data and 'data' in app_data:
+            data = app_data['data']
+        else:
             data = self
         return to_primitive(self.__class__, data, role=role, app_data=app_data, export_level=NOT_NONE, **kwargs)
 

schematics/transforms.py

@@ -234,7 +234,7 @@ def _mutate(schema, mutable, raw_data, context):
 
 
 def export_loop(schema, instance_or_dict, field_converter=None, role=None, raise_error_on_role=True,
-                export_level=None, app_data=None, context=None):
+                export_level=None, app_data=None, context=None, skip_fields=None):
     """
     The export_loop function is intended to be a general loop definition that
     can be used for any form of data shaping, such as application of roles or
@@ -292,10 +292,15 @@ def export_loop(schema, instance_or_dict, field_converter=None, role=None, raise
 
     if isinstance(instance_or_dict, models.Model):
         instance_or_dict = instance_or_dict._Model__data
+    
+    fields_to_skip = skip_fields if skip_fields is not None else []
 
     for field_name, field, value in atoms(schema, instance_or_dict):
         serialized_name = field.serialized_name or field_name
 
+        if serialized_name in fields_to_skip:
+            continue
+
         if filter_func is not None:
             value = filter_func(field_name, value, context)
             if value is ForbiddenRole: