Reach main urls.py and use another app url - django

Question

I have use 2 apps in my project named post and gallery. In url localhost:8000/en, I am using post.urls specifically "homepage". In homepage, when I want go to {% url "gallery:gallery_detail" "photos" %} it gives me an error. Because even though it takes a keyword "photos" it can not find any pattern specifically "gallery_detail".
My question is how can I reach this anathor app's url ?
My main urls.py:
from django.conf.urls import url,include
from django.conf import settings
from django.conf.urls.static import static
from django.conf.urls.i18n import i18n_patterns
from django.contrib import admin
urlpatterns = [
url(r'^admin/', admin.site.urls),
url(r'^ckeditor/', include("ckeditor_uploader.urls")),
]
urlpatterns += i18n_patterns(
url(r'^gallery/', include("gallery.urls",namespace="gallery")),
url(r'^', include("post.urls", namespace="post")),
)
urlpatterns += static(settings.STATIC_URL, document_root=settings.STATIC_ROOT)
urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)
My post.urls:
from django.conf.urls import url
from post.views import HomePageDetailView, AboutDetailView, \
CategoryDetailView, SponsorshipDetailView, CommonDetailView, NewsEntryDetailView
urlpatterns = [
url(r'^$', HomePageDetailView.as_view(), name="homepage"),
url(r'^about/(?P<slug>[-_\w]+)/$', AboutDetailView.as_view(),
name="about_detail"),
url(r'^category/(?P<slug>[-_\w]+)/$', CategoryDetailView.as_view(),
name="category_detail"),
url(r'^sponsorship/(?P<slug>[-_\w]+)/$', SponsorshipDetailView.as_view(),
name="sponsorship_detail"),
url(r'^news/(?P<slug>[-_\w]+)/$', NewsEntryDetailView.as_view(),
name="news_detail"),
url(r'^(?P<slug>[-_\w]+)/$', CommonDetailView.as_view(),
name="common_detail"),
]
My gallery.urls:
from django.conf.urls import url
from gallery.views import GalleryDetailView
urlpatterns = [
url(r'^(?P<slug>[-_\w]+)/$', GalleryDetailView.as_view(),
name="galery_detail"),
]