modelform_factory returns a broken form when given wrong value for fields

[ben]

modelform_factory is breaking where you ask for an invalid fields option (even if the field exists):

Here's a doctest that demonstrates:

from django.forms.models import modelform_factory, form_for_fields
from django.contrib.auth.models import User
Form = modelform_factory(User, fields=['id', 'username'])
Form.base_fields

{'id': None, 'username': <django.forms.fields.CharField object at 0xd4e4ad0>}

print Form()

---

Traceback (most recent call last):

...

if self.field.label is None:

AttributeError: 'NoneType' object has no attribute 'label'

Likewise you can specify fields that don't even exist on the model:

Form = modelform_factory(User, fields=['no-field', 'username'])
Form.base_fields

{'no-field': None, 'username': <django.forms.fields.CharField object at 0xd4eec10>}

print Form()

---

Traceback (most recent call last):

...

if self.field.label is None:

AttributeError: 'NoneType' object has no attribute 'label'

This appears to be due to logic in form_for_fields (line 102 in my checkout) in the first case, and fields_for_model (line 170) in the second.

I'd propose some error handling be put in place to give meaningfull exception in either of these cases rather than return a broken form to the user.

I'm happy to submit a patch (I can't do it from here as I'm at work and don't have direct access to django's svn repo) but I can do it from home.

Ben