Changed a few fields to be optional.

Found a fairly difficult bug involved with Field instances
being shared across Records. The issue is that Field instances
are static. I either need to implement a way to instantiate
copies of all the Fields per-record, or write a wrapping
interface which provides a unique value store on a per-Record
basis.

pyaccuwage/model.py

@@ -1,10 +1,12 @@
-from fields import Field
+from fields import Field, FieldWrapper
 
 class Model(object):    
     record_identifier = '  '
     required = False
 
     def __init__(self):
+        self.value_dict = {}
+
         for (key, value) in self.__class__.__dict__.items():
             if isinstance(value, Field):
                 field = getattr(self, key)
@@ -13,11 +15,19 @@ class Model(object):
                 setattr(field, 'parent_name', self.__class__.__name__)
 
     def __setattr__(self, key, value):
+        print "Model.__setattr__", self, key, value
         if hasattr(self, key) and isinstance(getattr(self, key), Field):
             getattr(self, key).value = value
         else:
             self.__dict__[key] = value
 
+    def __getattribute__(self, key):
+        result = object.__getattribute__(self, key)
+        if isinstance(result, Field):
+            return FieldWrapper(self.value_dict, result)
+        return result
+
+
     def get_fields(self):
         fields = []
         for key in self.__class__.__dict__.keys():