In a Django form, how do I make a field readonly (or disabled) so that it cannot be edited?

As pointed out in this answer, Django 1.9 added the Field.disabled attribute:

The disabled boolean argument, when set to True, disables a form field using the disabled HTML attribute so that it won’t be editable by users. Even if a user tampers with the field’s value submitted to the server, it will be ignored in favor of the value from the form’s initial data.

With Django 1.8 and earlier, to disable entry on the widget and prevent malicious POST hacks you must scrub the input in addition to setting the readonly attribute on the form field:

class ItemForm(ModelForm):
    def __init__(self, *args, **kwargs):
        super(ItemForm, self).__init__(*args, **kwargs)
        instance = getattr(self, 'instance', None)
        if instance and instance.pk:
            self.fields['sku'].widget.attrs['readonly'] = True

    def clean_sku(self):
        instance = getattr(self, 'instance', None)
        if instance and instance.pk:
            return instance.sku
        else:
            return self.cleaned_data['sku']

Or, replace if instance and instance.pk with another condition indicating you're editing. You could also set the attribute disabled on the input field, instead of readonly.

The clean_sku function will ensure that the readonly value won't be overridden by a POST.

Otherwise, there is no built-in Django form field which will render a value while rejecting bound input data. If this is what you desire, you should instead create a separate ModelForm that excludes the uneditable field(s), and just print them inside your template.

Django 1.9 added the Field.disabled attribute: https://docs.djangoproject.com/en/stable/ref/forms/fields/#disabled

The disabled boolean argument, when set to True, disables a form field using the disabled HTML attribute so that it won’t be editable by users. Even if a user tampers with the field’s value submitted to the server, it will be ignored in favor of the value from the form’s initial data.

Setting readonly on a widget only makes the input in the browser read-only. Adding a clean_sku which returns instance.sku ensures the field value will not change on form level.

def clean_sku(self):
    if self.instance: 
        return self.instance.sku
    else: 
        return self.fields['sku']

This way you can use model's (unmodified save) and avoid getting the field required error.