CssClassMixin for Django-Admin form elements

admin.py

class PostAdmin(CssClassMixin, admin.ModelAdmin):
    form_css_clasess = {
        'title': 'col-sm-8',
        'slug': 'col-sm-12'
    }

mixins.py

from django import forms


class CssClassMixin(object):
    def get_object_form(self, css_classes):
        model_class = self.model

        class _ObjectForm(forms.ModelForm):
            class Meta:
                model = model_class
                fields = '__all__'

            def __init__(self, *args, **kwargs):
                super(_ObjectForm, self).__init__(*args, **kwargs)

                for field in css_classes:
                    self.fields[field].widget.attrs['class'] = css_classes[field]

        return _ObjectForm

    def get_form(self, request, obj=None, **kwargs):
        return self.get_object_form(self.form_css_clasess)