Display OptGroup options from a Django ModelChoiceField

GroupedModelChoiceField

from django import forms

class GroupedModelChoiceField(forms.ModelChoiceField):

    def optgroup_from_instance(self, obj):
        return ""

    def __choice_from_instance__(self, obj):
	return (obj.id, self.label_from_instance(obj))

    def _get_choices(self):
        if not self.queryset:
            return []

        all_choices = []
	    if self.empty_label:
            current_optgroup = ""
            current_optgroup_choices = [("", self.empty_label)]
        else:
            current_optgroup = self.optgroup_from_instance(self.queryset[0])
            current_optgroup_choices = []

        for item in self.queryset:
            optgroup_from_instance = self.optgroup_from_instance(item)
            if current_optgroup != optgroup_from_instance:
                all_choices.append((current_optgroup, current_optgroup_choices))
                current_optgroup_choices = []
                current_optgroup = optgroup_from_instance
            current_optgroup_choices.append(self.__choice_from_instance__(item))

	    all_choices.append((current_optgroup, current_optgroup_choices))
	    return all_choices

    choices = property(_get_choices, forms.ChoiceField._set_choices)
    
class ExampleChoiceField(GroupedModelChoiceField):
    def optgroup_from_instance(self, obj):
    	return obj.group.name