Captcha widgets in Django

This blog was getting stormed by comment spam so i decided to use some captcha protection. I chose pycaptcha for this and had to integrate it nicely with Django. I wanted to make it an easy widget that does it’s own validation and does not require view code for validating the captcha. So here is what i came up with:

EDIT: Updated for SVN trunk version of Django ( value_from_datadict has an extra parameter)

First, the custom form field:


class CaptchaField(CharField):
    widget = CaptchaWidget
    def __init__(self, *args, **kwargs):
        super(CaptchaField, self).__init__(*args, **kwargs)


    def clean(self,values):
        value,captchaid = values
        #Check if the value matches that in the session
        factory = PersistentFactory('/tmp/captcha_persistence')
        test = factory.get(str(captchaid))
        factory.storedInstances.close()
        if (not test) or (not test.valid):
            raise ValidationError(u"""Captcha does not exist or is
            invalid. Please  refresh to get new captcha""")
        if not test.testSolutions([value.strip()]):
            raise ValidationError(u"""You did not type the correct
            captcha text""")
        return ""

The Widget used by this form field:


class CaptchaWidget(Input):
    input_type = "text"
    def render(self,name,value,attrs=None):
        #Always generate a new captcha on rendering
        factory = PersistentFactory('/tmp/captcha_persistence')
        test = factory.new(Tests.PseudoGimpy)
        factory.storedInstances.close()
        captchaid = test.id
        superclass_output = super(CaptchaWidget,self).render(name,"",attrs)
        output = """<img src="/captcha/%s" border="0"/><br/>
                    <input type="hidden" name="captchaid" value="%s" />
        %s
        """ %(captchaid,captchaid,superclass_output)
        return output

    def value_from_datadict(self,data,files,name):
        return [ data[name],data['captchaid'] ]


We also need a view to deliver the image for the captcha so here it is:

def captcha_image(request,id):

    factory = PersistentFactory('/tmp/captcha_persistence')
    test = factory.get(str(id))
    factory.storedInstances.close()
    if not test:
        return HttpResponseNotFound()

    response = HttpResponse(mimetype='image/jpeg')
    test.render().save(response,'JPEG')
    return response


Dont forget to add a urls.py entry for our view. something like:

(r'^captcha/(?P<id>\w+)','blogon.blog.views.captcha_image'),

should be enough (change the view to your view. If you change the url then be sure to change it in the html generated by the widget.

. Notice that in our code we use a file in /tmp for writing the persistence of pycaptcha. This may be a security problem depending on our environment. So be careful, or us a trusted location.
I should use a template for the HTML generated by the widget so as to make it more easily customizable but i just got bored after i got it working.