def mathCaptcha(request):       
    sign = random.choice("+-x")
    
    if(sign == "+"):
        num1 = random.randint(1,9)
        num2 = random.randint(1,9)
        request.session['captcha'] = num1 * num2
    else:
        num1 = random.randint(20,40)
        num2 = random.randint(1,20)
    
        if(sign == "+"):
            request.session['captcha'] = num1 + num2
        else:
            request.session['captcha'] = num1 - num2
            
    return str(num1) + sign + str(num2) + "="
class CommentForm(forms.Form):          
    name = forms.CharField(max_length=100, label='Имя', initial='Гость')
    email = forms.EmailField(required=False)
    text = forms.CharField(widget=forms.Textarea(), label='Сообщение')
    captcha = forms.CharField(label=mathCaptcha(request), validators=[validate_captcha])

def validate_captcha(value):
    if value != request.session['captcha']:
        raise ValidationError(u'%s неправильный ответ' % value)
class CommentForm(forms.Form):             
    name = forms.CharField(max_length=100, label='Имя', initial='Гость')
    email = forms.EmailField(required=False)
    text = forms.CharField(widget=forms.Textarea(), label='Сообщение')
    captcha = forms.CharField(validators=[validate_captcha])