I have 3 classes related to each other. A - B - C. B is related to pk of A and C is related to pk of B. URL structure?

Reverse for 'detail' with arguments '('',)' and keyword arguments '{}' not found. 1 pattern(s) tried: [u'taskoftheday/(?P<guide_id>[0-9]+)/$']

    url(r'^(?P<guide_id>[0-9]+)/$', views.detail, name='detail'),
    url(r'^(?P<step_id>[0-9]+)/complete/$', views.complete, name='complete'),
    url(r'^steps/(?P<filter_by>[a-zA_Z]+)/$', views.steps, name='steps'),
    url(r'^steps/(?P<filter_by>[a-zA_Z]+)/$', views.subtasks, name='subtasks'),
    url(r'^create_guide/$', views.create_guide, name='create_guide'),
    url(r'^(?P<guide_id>[0-9]+)/create_step/$', views.create_step, name='create_step'),
    url(r'^(?P<step_id>[0-9]+)/create_subtask/$', views.create_subtask, name='create_subtask'),
    url(r'^(?P<guide_id>[0-9]+)/delete_step/(?P<step_id>[0-9]+)/$', views.delete_step, name='delete_step'),
    url(r'^(?P<step_id>[0-9]+)/delete_subtask/(?P<subtask_id>[0-9]+)/$', views.delete_subtask, name='delete_subtask'),
    url(r'^(?P<guide_id>[0-9]+)/complete_guide/$', views.complete_guide, name='complete_guide'),
    url(r'^(?P<guide_id>[0-9]+)/delete_guide/$', views.delete_guide, name='delete_guide'),

def steps(request, filter_by):
    if not request.user.is_authenticated():
        return render(request, 'taskoftheday/login.html')
    else:
        try:
            step_ids = []
            for guide in Guide.objects.filter(user=request.user):
                for step in guide.step_set.all():
                    step_ids.append(step.pk)
            users_steps = Step.objects.filter(pk__in=step_ids)
            if filter_by == 'completes':
                users_steps = users_steps.filter(is_complete=True)
        except Guide.DoesNotExist:
            users_steps = []
        return render(request, 'taskoftheday/steps.html', {
            'step_list': users_steps,
            'filter_by': filter_by,
        })


def subtasks(request, filter_by):
    if not request.user.is_authenticated():
        return render(request, 'taskoftheday/login.html')
    else:
        try:
            subtask_ids = []
            for step in Step.objects.filter(user=request.user):
                for subtask in step.subtask_set.all():
                    subtask_ids.append(subtask.pk)
            users_subtasks = Subtask.objects.filter(pk__in=subtask_ids)
            if filter_by == 'completes':
                users_subtasks = users_subtasks.filter(is_complete=True)
        except Guide.DoesNotExist:
            users_steps = []
        return render(request, 'taskoftheday/steps.html', {
            'step_list': users_subtasks,
            'filter_by': filter_by,
        })

def create_step(request, guide_id):
    form = StepForm(request.POST)
    guide = get_object_or_404(Guide, pk=guide_id)
    if form.is_valid():
        guides_steps = guide.step_set.all()
        for s in guides_steps:
            if s.step_title == form.cleaned_data.get("step_title"):
                context = {
                    'guide': guide,
                    'form': form,
                    'error_message': 'You already added that step',
                }
                return render(request, 'taskoftheday/create_step.html', context)
        step = form.save(commit=False)
        step.guide = guide
        step.save()
        return render(request, 'taskoftheday/detail.html', {'guide': guide})
    context = {
        'guide': guide,
        'form': form,
    }
    return render(request, 'taskoftheday/create_step.html', context)

def create_subtask(request, step_id):
    form = StepForm(request.POST)
    step = get_object_or_404(Step, pk=step_id)
    if form.is_valid():
        steps_subtasks = step.subtask_set.all()
        for s in steps_subtasks:
            if s.subtask_title == form.cleaned_data.get("subtask_title"):
                context = {
                    'step': step,
                    'form': form,
                    'error_message': 'You already added that subtask',
                }
                return render(request, 'taskoftheday/create_subtask.html', context)
        subtask = form.save(commit=False)
        subtask.step = step
        subtask.save()
        return render(request, 'taskoftheday/detail.html', {'step': step})
    context = {
        'step': step,
        'form': form,
    }
    return render(request, 'taskoftheday/create_subtask.html', context)