Django form using super() and queryset

forms.py

class ArticleUpdateForm(ModelForm):
    """
    Form for updating an article.
    """
    def __init__(self, *args, **kwargs):
        super(ArticleUpdateForm, self).__init__(*args, **kwargs)

        self.fields['attachments'] = forms.ModelMultipleChoiceField(
            queryset=self.instance.attachments.all(), required=False
        )

        self.fields['versioning_mode'] = forms.ChoiceField(
            label='Save new versions as',
            choices=(
                ('Minor', 'Minor'),
                ('Major', 'Major'),
            ),
        )

        self.fields['content'] = forms.CharField(
            widget=forms.Textarea(attrs={'class': 'content_textarea'}),
            initial=self.instance.get_latest_content(),
        )

        self.fields['project'] = forms.ModelChoiceField(
            queryset=Project.objects.filter(allow_articles=True),
            required=False
        )

    class Meta:
        model = Article
        widgets = {'description': forms.Textarea(attrs={'rows':6, 'cols':89}),}
        fields = [
            'title', 'audience', 'is_published', 'project',
            'description', 'attachments',
        ]