Django, Class Based View, Helper

a.py

from django.core.urlresolvers import reverse


class PostUpdateView(BaseUpdateView):
    model = Post
    form_class = PostForm

    # template_context = {'form_title': 'form title'}
    template_context = lambda self: {'form_title': '<%s> edit' % self.object.name}

    # valid_message = lambda self: 'updated'
    # valid_message = lambda self: ('info', '<%s> updated' % self.get_object().name)
    valid_message = lambda self: [
        ('info', '<%s> updated' % self.get_object().name),
        ('debug', '<%s> updated (debug)' % self.get_object().name),
    ]

    success_url_fn = lambda self: reverse('post:detail', args=[self.object.id])

generic.py

from django.contrib import messages as django_messages
from django.utils import six
from django.views.generic import ListView, DetailView, CreateView, UpdateView, DeleteView
from django.views.generic.base import ContextMixin
from django.views.generic.edit import FormMixin


MESSAGE_LEVELS = {
    'debug': django_messages.DEBUG,
    'info': django_messages.INFO,
    'success': django_messages.SUCCESS,
    'warning': django_messages.WARNING,
    'error': django_messages.ERROR,
}


class BaseContextMixin(ContextMixin):
    template_context = {}

    def get_context_data(self, *args, **kwargs):
        data = super(BaseContextMixin, self).get_context_data(*args, **kwargs)
        if callable(self.template_context):
            data.update(self.template_context())
        else:
            data.update(self.template_context)
        return data


class BaseFormMixin(FormMixin):
    valid_message = None
    success_url_fn = None

    def form_valid(self, form):
        response = super(BaseFormMixin, self).form_valid(form)

        if self.valid_message is not None:
            if callable(self.valid_message):
                messages = self.valid_message()
            else:
                messages = self.valid_message

            if not isinstance(messages, (tuple, list)):
                messages = [messages]

            for row in messages:
                if callable(row):
                    row = row(self)

                if isinstance(row, (tuple, list)):
                    level, message = row
                else:
                    level = django_messages.INFO
                    message = row

                if isinstance(level, six.string_types):
                    try:
                        level = MESSAGE_LEVELS[level]
                    except KeyError:
                        pass

                django_messages.add_message(self.request, level, message)

        return response

    def get_success_url(self):
        if callable(self.success_url_fn):
            self.success_url = self.success_url_fn()
        return super(BaseFormMixin, self).get_success_url()


class BaseListView(BaseContextMixin, ListView):
    pass


class BaseDetailView(BaseContextMixin, DetailView):
    pass


class BaseCreateView(BaseContextMixin, BaseFormMixin, CreateView):
    pass


class BaseUpdateView(BaseContextMixin, BaseFormMixin, UpdateView):
    pass


class BaseDeleteView(BaseContextMixin, BaseFormMixin, DeleteView):
    pass