django input element error css class

Using a Custom Template...

Personally never had much luck using the built in Django error classing solutions, and besides, I like to use the built in 'striptags' template filter on the errors, to get rid of all the html list stuff which I cant figure out how to render nicely anyway.

I use the following custom template to class them as 'error_id'.

@register.filter(is_safe=True)
@stringfilter
def error_id(value):
    if value=='':
        return ''
    else:
        return r'<span class="error_id">'+value+'</span>'

Render the individual errors in your template using:

{{ form.my_field.errors|striptags|error_id}}

Or render the whole form using something like:

    <table border="1" cellpadding="5px" align="center">
        {% for field in form.visible_fields %}
            <tr>
                        <td> {{ field.label_tag }}: </td>
                        <td>    {{ field }}  </td>
                        <td> {{ field.errors|striptags|error_id }} </td>
            </tr>

        {% endfor %}

    </table>

This can be done completely through your template.

You build the form template for each form field that you want to test you can use the following example construct

<input type="text" class="reg-txt{% if form.fieldname.errors %} errors{% endif %}"/>

This lets you provide the interface you want without modifying the view & django form code.

If you want to place your error CSS class to form input widgets (not their containers), you can derive your form class from the following one:

class StyledErrorForm(forms.Form):
     def is_valid(self):
         result = super().is_valid()
         # loop on *all* fields if key '__all__' found else only on errors:
         for x in (self.fields if '__all__' in self.errors else self.errors):
             attrs = self.fields[x].widget.attrs
             attrs.update({'class': attrs.get('class', '') + ' is-invalid'})
         return result

It's now easy -- new feature in Django 1.2

Just add an attribute on the form class & you're good to go. This feature is mentioned in the docs under a "new in 1.2" note, but you can find the magic at django.forms.forms.BoundField.css_classes Here's the API reference, and an example:

class MyForm(forms.Form):
    required_css_class = "required"
    error_css_class = "error"