Fixed #3334 -- Changed newforms Form class construction so that appending to (or altering) self.fields affects only the instance, not the class. As a consequence, self.fields is created in Form.__init__(). The form metaclass now creates a variable self.base_fields instead of self.fields.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4437 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/newforms/forms.py

@@ -26,12 +26,15 @@ class SortedDictFromList(SortedDict):
         self.keyOrder = [d[0] for d in data]
         dict.__init__(self, dict(data))
 
+    def copy(self):
+        return SortedDictFromList(self.items())
+
 class DeclarativeFieldsMetaclass(type):
-    "Metaclass that converts Field attributes to a dictionary called 'fields'."
+    "Metaclass that converts Field attributes to a dictionary called 'base_fields'."
     def __new__(cls, name, bases, attrs):
         fields = [(field_name, attrs.pop(field_name)) for field_name, obj in attrs.items() if isinstance(obj, Field)]
         fields.sort(lambda x, y: cmp(x[1].creation_counter, y[1].creation_counter))
-        attrs['fields'] = SortedDictFromList(fields)
+        attrs['base_fields'] = SortedDictFromList(fields)
         return type.__new__(cls, name, bases, attrs)
 
 class BaseForm(StrAndUnicode):
@@ -46,6 +49,12 @@ class BaseForm(StrAndUnicode):
         self.prefix = prefix
         self.initial = initial or {}
         self.__errors = None # Stores the errors after clean() has been called.
+        # The base_fields class attribute is the *class-wide* definition of
+        # fields. Because a particular *instance* of the class might want to
+        # alter self.fields, we create self.fields here by copying base_fields.
+        # Instances should always modify self.fields; they should not modify
+        # self.base_fields.
+        self.fields = self.base_fields.copy()
 
     def __unicode__(self):
         return self.as_table()

django/newforms/models.py

@@ -64,7 +64,7 @@ def form_for_model(model, form=BaseForm, formfield_callback=lambda f: f.formfiel
         if formfield:
             field_list.append((f.name, formfield))
     fields = SortedDictFromList(field_list)
-    return type(opts.object_name + 'Form', (form,), {'fields': fields, '_model': model, 'save': model_save})
+    return type(opts.object_name + 'Form', (form,), {'base_fields': fields, '_model': model, 'save': model_save})
 
 def form_for_instance(instance, form=BaseForm, formfield_callback=lambda f, **kwargs: f.formfield(**kwargs)):
     """
@@ -87,9 +87,9 @@ def form_for_instance(instance, form=BaseForm, formfield_callback=lambda f, **kw
             field_list.append((f.name, formfield))
     fields = SortedDictFromList(field_list)
     return type(opts.object_name + 'InstanceForm', (form,),
-        {'fields': fields, '_model': model, 'save': make_instance_save(instance)})
+        {'base_fields': fields, '_model': model, 'save': make_instance_save(instance)})
 
 def form_for_fields(field_list):
     "Returns a Form class for the given list of Django database field instances."
     fields = SortedDictFromList([(f.name, f.formfield()) for f in field_list])
-    return type('FormForFields', (BaseForm,), {'fields': fields})
+    return type('FormForFields', (BaseForm,), {'base_fields': fields})