def math_clean(form):
"""
Cleans a form, validating answer to math question in the process.
The given ``form`` must be an instance of either ``MathCaptchaModelForm`` or ``MathCaptchaForm``.
Answer keys are communicated in the ``math_captcha_question`` field which is evaluated to give the correct answer
after being validated against the ``SECRET_KEY``
"""
try:
value = form.cleaned_data['math_captcha_field']
test_secret, question = decode(form.cleaned_data['math_captcha_question'])
assert len(test_secret) == 40 and question
except (TypeError, AssertionError):
# problem decoding, junky data
raise forms.ValidationError('Invalid token')
except KeyError:
return
if encode(question) != form.cleaned_data['math_captcha_question']:
# security problem, hack attempt
raise forms.ValidationError('Invalid token')
if eval(question) != value:
raise forms.ValidationError('Wrong answer, try again')
def render(self, name, value, attrs):
aquestion = question()
value = super(MathWidget, self).render(name, value, attrs)
hidden = '<input type="hidden" value="%s" name="math_captcha_question"/>' % encode(aquestion)
return value.replace('<input', '%s %s = <input' % (hidden, aquestion))
