Custom form widget for add additional attributes to option tags of select on Django forms.

form_widgets.py

from django import forms
from django.utils.encoding import force_text
from django.utils.html import format_html
from django.utils.safestring import mark_safe


class SelectOptionsWithAttrs(forms.widgets.Select):
    def render_options(self, selected_choices):
        # Normalize to strings.
        selected_choices = set(force_text(v) for v in selected_choices)
        output = []
        
        try:
            for option_value, option_label, option_attrs in self.choices:
                output.append(self.render_option(selected_choices, option_value, option_label, option_attrs))
            return '\n'.join(output)
        except ValueError:
            # Select has optgroups or has not any additional attributes
            return super(SelectWithAttrs, self).render_options(selected_choices)

    def render_option(self, selected_choices, option_value, option_label, option_attrs=None):

        if option_value is None:
            option_value = ''
        option_value = force_text(option_value)

        if not option_attrs:
            option_attrs = {}

        attrs_html = ''
        for attr_key, attr_val in option_attrs.items():
            attrs_html += ' {}="{}"'.format(attr_key, attr_val)
        attrs_html = mark_safe(attrs_html)

        if option_value in selected_choices:
            selected_html = mark_safe(' selected="selected"')
            if not self.allow_multiple_selected:
                # Only allow for a single selection.
                selected_choices.remove(option_value)
        else:
            selected_html = ''
            
        return format_html(
            '<option value="{}"{}{}>{}</option>',
            option_value,
            selected_html,
            attrs_html,
            force_text(option_label)
        )

forms.py

from django import forms
from form_widgets import SelectOptionsWithAttrs

class ExampleForm(forms.Form):
    foo = forms.ChoiceField(label='Foo', widget=SelectOptionsWithAttrs())

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

        choices = (
            (1, 'mytext', {'class': 'foo bar', 'data-type': 'my-type', 'data-foo': 'bar'},),
            (2, 'mytext2', {'class': 'bar baz', 'data-type': 'my-other-type', 'data-foo': 'bar2'},),
        )

        self.fields['foo'].choices = choices

# Rendered html of the form field
# <select id="id_foo" name="foo">
#    <option value="1" class="foo bar" data-foo="bar" data-type="my-type">mytext</option>
#    <option value="2" class="foo baz" data-foo="bar2" data-type="my-other-type">mytext2</option>
# </select>