在工程文件中url 定義namespace需要

from django.contrib import admin
from django.urls import path,include
from django.conf.urls import url
urlpatterns = [path('admin/', admin.site.urls),url(r'^liu/',include('myApp.urls',namespace='app')),
]

在myApp 的urls中 加這句 app_name='[myApp]'

from . import views
app_name='[myApp]'
urlpatterns = [url(r'^$', views.index,name="index"),url(r'index.html', views.index1),