Not sure why it is giving me a name error

from django.shortcuts import get_object_or_404, render
from .models import Course 


# Create your views here.
def course_list(request):
    courses = Course.objects.all()
    return render(request, 'courses/course_list.html', {'courses': courses})

def course_detail(request, pk):
    course = get_object_or_404(Course, pk=pk)
    return render(request, 'courses/course_detail.html', {'course': course})

def step_detail(request, course_pk, step_pk):
    step = get_object_or_404(Step, course_id=course_pk, pk=step_pk)
    return render(request, 'courses/step_detail.html', {'step': step})

from django.contrib import admin

# Register your models here.
from .models import Course, Step

class StepInline(admin.StackedInline):
    model = Step


class CourseAdmin(admin.ModelAdmin):
    inlines = [StepInline,]

admin.site.register(Course, CourseAdmin)
admin.site.register(Step)

from django.db import models

# Create your models here.
class Course(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    title = models.CharField(max_length=255)
    description = models.TextField()

    def __str__(self):
        return self.title

class Step(models.Model):
    title = models.CharField(max_length=255)
    description = models.TextField()
    order = models.IntegerField(default=0)
    course = models.ForeignKey(Course)

    class Meta:
        ordering = ['order',]

    def __str__(self):
        return self.title

from django.conf.urls import url, include

from . import views

urlpatterns = [
    url(r'^$', views.course_list),
    url(r'(?P<course_pk>\d+)/(?P<step_pk>\d+)/$', views.step_detail),
    url(r'(?P<pk>\d+)/$', views.course_detail),
]