我的代码：

class RegisterForm(forms.Form):

   email = forms.EmailField(required=True)
   password = forms.CharField(required=True, min_length=5)
   captcha = CaptchaField(error_messages={"invalid": u"验证码错误"})

def post(self, request):
   register_form = RegisterForm(request.POST)
   if register_form.is_valid():
       email = request.POST.get("email", "")
       password = request.POST.get("password", "")    
       user_profile = UserProfile()
       user_profile.username = email
       user_profile.email = email
       user_profile.password = make_password(password)
       user_profile.save()
       return render(request, "login.html", {})
   else:
       return render(request, 'register.html', {'register_form': register_form})

debug显示：<ul class="errorlist"><li>这个字段是必填项。</li></ul>