include(router.urls, namespace='api_router') - throwing error cannot import api_router. Whereas its just a namespace

from django.conf.urls import url, include
from django.contrib import admin

from rest_framework import routers

from scorekeeper import views

router = routers.SimpleRouter()
router.register(r'players', views.PlayerViewSet)

urlpatterns = [
    url(r'^api/v1/', include('scorekeeper.urls', namespace='scorekeeper')),
    url(r'^api/v2/', include(router.urls, namespace='api_router')),
]

from rest_framework import generics
from rest_framework import viewsets

from . import models
from . import serializers


class GameListCreate(generics.ListCreateAPIView):
    queryset = models.Game.objects.all()
    serializer_class = serializers.GameSerializer


class GameScoresList(generics.ListAPIView):
    queryset = models.Score.objects.all()
    serializer_class = serializers.ScoreSerializer

    def get_queryset(self):
        return self.queryset.filter(
            game_id=self.kwargs.get('game_pk')
        )


class PlayerViewSet(viewsets.ModelViewSet):
    queryset = models.Player.objects.all()
    serializer_class = serializers.PlayerSerializer