class ModelBrowseField(forms.ChoiceField):
    """
    Browse through the installed models using the content types framework.
    There are two difference in behavior with respect to the default field:

      1. if a model provides a translation (e.g.: verbose_name and/or
         verbose_name_plural), we show that rather than a raw model name
      2. allow to filter the models shown
    """
    def __init__(self, choices=None, *args, **kwargs):
        from django.contrib.contenttypes.models import ContentType

        qs = ContentType.objects.all()
        if choices:
            # if there's a list of allowed models, filter the queryset
            choices = list(choices)

            # labels are all lowercase
            choices = [choice.lower() for choice in choices]
            qs = qs.filter(model__in=choices)

        choices = qs.values_list('id', 'name')

        # translate items (if available)
        newchoices = []
        for id, choice in choices:
            id, mclass = id, ContentType.objects.get(pk=id).model_class()
            if mclass:
                newchoices.append((id, mclass._meta.verbose_name))
        choices = newchoices

        choices.insert(0, ('', '---------'))
        super(ModelBrowseField, self).__init__(choices=choices, *args, **kwargs)