Keep Package.fields() method used in CSV output

Signed-off-by: Philippe Ombredanne <[email protected]>

Author: pombredanne

src/packagedcode/models.py

@@ -87,11 +87,19 @@ def create(cls, **kwargs):
         provided in ``kwargs`` that do not exist as declared attr fields in
         ``cls``.
         """
-        known_attr = attr.fields_dict(cls)
+        known_attr = cls.fields()
         kwargs = {k: v for k, v in kwargs.items() if k in known_attr}
         return cls(**kwargs)
 
 
+    @classmethod
+    def fields(cls):
+        """
+        Return a list of field names defined on this model.
+        """
+        return list(attr.fields_dict(cls))
+
+
 party_person = 'person'
 # often loosely defined
 party_project = 'project'