求助 ValueError at /form/ The view tools.views.TestForm didn't return an HttpResponse object. It returned None instead.

目标：使用django forms表单实现两个参数的求和 实现代码： forms.py from django import forms

class AddForm(forms.Form): a=forms.IntegerField() b=forms.IntegerField()

views.py from django.shortcuts import render from django.http import HttpResponse

from .forms import AddForm

def TestForm(request): if request.method=='POST': form=AddForm(request.POST)

    if form.is_valid():
        a=form.cleaned_data['a']
        b=form.cleaned_data['b']
        return HttpResponse(str(int(a)+int(b)))
    else:
        form=AddForm()
    return render(request,'index.html',{'form':form})

index.html <form method='post'> {% csrf_token %} {{form}} <input type="submit" value="提交"> </form>

urls.py from django.conf.urls import url from django.contrib import admin from tools.views import TestForm

urlpatterns =[ url(r'^admin/', admin.site.urls), url(r'^form/',TestForm,name='testform'), ]

希望大神能指导如何分析该报错信息，并且根据报错信息到源码去找到错误处？