se separa responsabilidad de fields.Function

FossilOrigin-Name: 4d5daa47a75a0e283e86bf992126bf60f3a8a14287e9acc437d5f2f3eca43150

facho/model/fields/attribute.py

@@ -1,17 +1,18 @@
 from .field import Field
 
 class Attribute(Field):
-    def __init__(self, tag):
+    def __init__(self, tag, default=None):
         self.tag = tag
-  
+        self.value = default
+
     def __get__(self, inst, cls):
         if inst is None:
             return self
 
         assert self.name is not None
-        (tag, value) =  inst._xml_attributes[self.name]
-        return value
+        return self.value
 
     def __set__(self, inst, value):
         assert self.name is not None
+        self.value = value
         inst._xml_attributes[self.name] = (self.tag, value)