无法将django-recaptcha添加到注册表单中

Question

我在将django-recaptcha添加到注册表单时遇到问题。该表格是django-registration表格的延伸。这是我插入的方式（仅显示相关代码）：

urls.py：

from registration_custom.forms import RegistrationFormUniqueEmail

url(r'^accounts/register/$', 'registration_custom.views.register',
{'form_class':RegistrationFormUniqueEmail,
    'backend':'registration.backends.default.DefaultBackend' }, name='registration_register',),

* registration_custom.forms.py：*

from captcha.fields import ReCaptchaField 

class RegistrationFormUniqueEmail(RegistrationForm):
    """
    Subclass of ``RegistrationForm`` which enforces uniqueness of
    email addresses.

    """
    # added recaptcha
    captcha = ReCaptchaField()

    def clean_email(self):
        """
        Validate that the supplied email address is unique for the
        site.

        """
        if User.objects.filter(email__iexact=self.cleaned_data['email']):
        raise forms.ValidationError(_("This email address is already in use. Please supply a different email address."))
        return self.cleaned_data['email']

我已经检查过，看看我的重新密钥是否正确，它们是否正确，并且为我正在测试的域设置了密钥。

你能发现我错过的东西吗？感谢。