field and widget

# -*- coding: utf-8 -*-

from django import forms
from django.utils.html import escape, conditional_escape
from django.utils.encoding import force_unicode


def get_attr(obj, attr):
    if hasattr(obj, attr):
        res = getattr(obj, attr)
        if hasattr(res, '__call__'):
            return res()
        else:
            return res
    return ''


class SelectWithData(forms.Select):
    def render_option(self, selected_choices, option_value, option_label):
        data_text = u''
        option_value = force_unicode(option_value)

        if self.queryset is None:
            self.queryset = self.get_queryset()

        if option_value:
            obj = next(x for x in self.queryset if unicode(x.pk) == option_value)
            obj_data = {
                data_attr: get_attr(obj, data_attr) for data_attr in self.data_attrs
            }

            for data_attr in self.data_attrs:
                data_text += u' data-{}="{}" '.format(
                    data_attr,
                    escape(force_unicode(obj_data[data_attr]))
                )

        selected_html = (option_value in selected_choices) and u' selected="selected"' or ''
        return u'<option value="{}"{}{}>{}</option>'.format(
            escape(option_value),
            data_text,
            selected_html,
            conditional_escape(force_unicode(option_label))
        )


class ModelChoiceFieldWithData(forms.ModelChoiceField):
    widget = SelectWithData

    def __init__(self, queryset, get_queryset=None, **kwargs):
        data_attrs = kwargs.pop('data_attrs')
        super(ModelChoiceFieldWithData, self).__init__(queryset, **kwargs)

        if get_queryset is None:
            self.widget.queryset = queryset
            self.widget.get_queryset = None
        else:
            self.widget.queryset = None
            self.widget.get_queryset = get_queryset

        self.widget.data_attrs = data_attrs
        

forms

class OrderForm(forms.ModelForm):
    city = ModelChoiceFieldWithData(
        required=False,
        data_attrs=('id','slug',),
        queryset=City.objects.all(),
        get_queryset=lambda: City.objects.all().prefetch_related('cityshipping_set'),
    )
    
    shipping = ModelChoiceFieldWithData(
        required=False,
        data_attrs=('price',),
        queryset=Shipping.objects.all(),
    )

html

<select id="id_city" name="city" title="">
  <option value="1" data-id="1" data-slug="moskva" selected="selected">Moscow</option>
  <option value="2" data-id="2" data-slug="piter" selected="selected">Saint-Petersburg</option>
</select>

<select id="id_shipping" name="shipping" title="">
  <option value="1" data-price="100">Fast Delivery</option>
  <option value="2" data-price="200">Slow Shipping</option>
</select>