Ticket #5050: newforms_metaclassing.patch

django/newforms/forms.py

@@ -33 +33 @@
     def copy(self):
         return SortedDictFromList([(k, copy.copy(v)) for k, v in self.items()])
 
-class DeclarativeFieldsMetaclass(type):
+class BaseFieldsMetaclass(type):
     """
-    Metaclass that converts Field attributes to a dictionary called
-    'base_fields', taking into account parent class 'base_fields' as well.
+    Metaclass that ensures attrs will have a dictionary called 'base_fields',
+    built on the parent class '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))
-
-        # If this class is subclassing another Form, add that Form's fields.
+        fields = attrs.get('base_fields', {}).items()
+        # If this class is subclassing another BaseForm, add that form's fields.
         # Note that we loop over the bases in *reverse*. This is necessary in
         # order to preserve the correct order of fields.
         for base in bases[::-1]:
             if hasattr(base, 'base_fields'):
                 fields = base.base_fields.items() + fields
-
-        attrs['base_fields'] = SortedDictFromList(fields)
+        attrs['base_fields'] = SortedDictFromList(fields)        
         return type.__new__(cls, name, bases, attrs)
 
+class DeclarativeFieldsMetaclass(BaseFieldsMetaclass):
+    """
+    Metaclass that converts Field attributes to the dictionary attribute called
+    'base_fields' created by BaseFieldsMetaclass.
+    """
+    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))        
+
+        newcls = BaseFieldsMetaclass.__new__(cls, name, bases, attrs)
+
+        for k, v in fields:
+            newcls.base_fields[k] = v
+
+        return newcls
+
 class BaseForm(StrAndUnicode):
     # This is the main implementation of all the Form logic. Note that this
     # class is different than Form. See the comments by the Form class for more
     # information. Any improvements to the form API should be made to *this*
     # class, not to the Form class.
+    __metaclass__ = BaseFieldsMetaclass
     def __init__(self, data=None, auto_id='id_%s', prefix=None, initial=None):
         self.is_bound = data is not None
         self.data = data or {}

tests/modeltests/model_forms/models.py

@@ -526 +526 @@
 True
 >>> f.cleaned_data
 {'phone': u'312-555-1212', 'description': u'Assistance'}
+
+
+# Multiple subclasses #########################################################
+
+>>> WriterForm = form_for_model(Writer)
+>>> PhoneNumberForm = form_for_model(PhoneNumber)
+>>> class MixinForm(WriterForm, PhoneNumberForm):
+...     pass
+>>> print MixinForm(auto_id=None).base_fields.keys()
+['name', 'phone', 'description']
 """}