Implementing a Multiple (Radio) Select + “Other” widget in Django

I have had a task to implement Radio Select field with "Other" choice field in a Django Model Form. Here is my implementation in case someone would benefit from it. The idea is to have it all stored to Django's CharField type of data and have a preselected set of fields. We have a model:

# models.py
class Entry(models.Model):

    SET_OF_CHOICES = (
        ('choice1', 'choice1'),
        ('choice2', 'choice2'),
        ('choice3', 'choice3'),
        ('Other', 'Other Please Specify'),
    )

    choice = models.CharField(_("Selected your choice"), max_length=250)

That makes it ready for the set of fields for for our form. We are overriding Model form default field for this type of data (CharField) by intentionally specifying field with the same name.

# forms.py
from django.forms import ModelForm, ChoiceField, RadioSelect
from models import Entry
from fields import ChoiceWithOtherField


class EntryForm(ModelForm):

    choice = ChoiceWithOtherField(label=_("Selected your choice"), choices=Entry.SET_OF_CHOICES)

Note the field.py import here. We are using custom form field here. It is a modified version of Django's
MultiValueField.
Here is the fields snippet:

# fields.py
from django import newforms as forms
from django.utils.encoding import force_unicode


class ChoiceWithOtherRenderer(forms.RadioSelect.renderer):
    """RadioFieldRenderer that renders its last choice with a placeholder."""
    def __init__(self, *args, **kwargs):
        super(ChoiceWithOtherRenderer, self).__init__(*args, **kwargs)
        self.choices, self.other = self.choices[:-1], self.choices[-1]

    def __iter__(self):
        for input in super(ChoiceWithOtherRenderer, self).__iter__():
            yield input
        id = '%s_%s' % (self.attrs['id'], self.other[0]) if 'id' in self.attrs else ''
        label_for = ' for="%s"' % id if id else ''
        checked = '' if not force_unicode(self.other[0]) == self.value else 'checked="true" '
        yield '<label%s><input type="radio" id="%s" value="%s" name="%s" %s/> %s</label> %%s' % (
            label_for, id, self.other[0], self.name, checked, self.other[1])


class ChoiceWithOtherWidget(forms.MultiWidget):
    """MultiWidget for use with ChoiceWithOtherField."""
    def __init__(self, choices):
        widgets = [
            forms.RadioSelect(choices=choices, renderer=ChoiceWithOtherRenderer),
            forms.TextInput
        ]
        super(ChoiceWithOtherWidget, self).__init__(widgets)

    def decompress(self, value):
        if not value:
            return [None, None]
        return value

    def format_output(self, rendered_widgets):
        """Format the output by substituting the "other" choice into the first widget."""
        return rendered_widgets[0] % rendered_widgets[1]


class ChoiceWithOtherField(forms.MultiValueField):
    """
    ChoiceField with an option for a user-submitted "other" value.

    The last item in the choices array passed to __init__ is expected to be a choice for "other". This field's
    cleaned data is a tuple consisting of the choice the user made, and the "other" field typed in if the choice
    made was the last one.

    >>> class AgeForm(forms.Form):
    ...     age = ChoiceWithOtherField(choices=[
    ...         (0, '15-29'),
    ...         (1, '30-44'),
    ...         (2, '45-60'),
    ...         (3, 'Other, please specify:')
    ...     ])
    ...
    >>> # rendered as a RadioSelect choice field whose last choice has a text input
    ... print AgeForm()['age']
    <ul>
    <li><label for="id_age_0_0"><input type="radio" id="id_age_0_0" value="0" name="age_0" /> 15-29</label></li>
    <li><label for="id_age_0_1"><input type="radio" id="id_age_0_1" value="1" name="age_0" /> 30-44</label></li>
    <li><label for="id_age_0_2"><input type="radio" id="id_age_0_2" value="2" name="age_0" /> 45-60</label></li>
    <li><label for="id_age_0_3"><input type="radio" id="id_age_0_3" value="3" name="age_0" /> Other, please \\
specify:</label> <input type="text" name="age_1" id="id_age_1" /></li>
    </ul>
    >>> form = AgeForm({'age_0': 2})
    >>> form.is_valid()
    True
    >>> form.cleaned_data
    {'age': (u'2', u'')}
    >>> form = AgeForm({'age_0': 3, 'age_1': 'I am 10 years old'})
    >>> form.is_valid()
    True
    >>> form.cleaned_data
    {'age': (u'3', u'I am 10 years old')}
    >>> form = AgeForm({'age_0': 1, 'age_1': 'This is bogus text which is ignored since I didn\\\\'t pick "other"'})
    >>> form.is_valid()
    True
    >>> form.cleaned_data
    {'age': (u'1', u'')}
    """
    def __init__(self, *args, **kwargs):
        fields = [
            forms.ChoiceField(widget=forms.RadioSelect(renderer=ChoiceWithOtherRenderer), *args, **kwargs),
            forms.CharField(required=False)
        ]
        widget = ChoiceWithOtherWidget(choices=kwargs['choices'])
        kwargs.pop('choices')
        self._was_required = kwargs.pop('required', True)
        kwargs['required'] = False
        super(ChoiceWithOtherField, self).__init__(widget=widget, fields=fields, *args, **kwargs)

    def compress(self, value):
        if self._was_required and not value or value[0] in (None, ''):
            raise forms.ValidationError(self.error_messages['required'])
        if not value:
            return [None, u'']
        # Patch to override model specific other choice and return CharField value instead of choice tuple
        if value[0] == 'Other':
            return value[1]
        else:
            return value[0]
        # Use this for field to return tuple
        #return value[0], value[1] if force_unicode(value[0]) == force_unicode(self.fields[0].choices[-1][0]) else u''

It is based on the code from the snippet by sciyoshi. It is put here because there are some modifications to in inline with idea that things could easily disappear without a trace through the internet.
Anyway it will show something like this in the end:

It's up to your imagination to style it now. Hope this howto helps someone with similar problem to save some time.