def edit(request,id):
    edit_obj=Book.objects.get(pk=id)
    if GET请求:
        form=BookModelForm(instance=edit_obj)
        return render(reqeust,{"form":form})
        '''
        渲染页面同添加页面
        '''
    else POST请求:
        form=BookModelForm(request.POST,instance=edit_obj)
        if form.is_valid():
            # edit_obj.update(clean_data)
            form.save()
            return redirect("/")
        else:
            return render(reqeust,{"form":form})