class FormMixin

def form_invalid(self, form):
    """
    If the form is invalid, re-render the context data with the
    data-filled form and errors.
    """
    return self.render_to_response(self.get_context_data(form=form))

def form_valid(self, form):
    """
    If the form is valid, redirect to the supplied URL.
    """
    return HttpResponseRedirect(self.get_success_url())

def get_form(self, form_class=None):
    """
    Returns an instance of the form to be used in this view.
    """
    if form_class is None:
        form_class = self.get_form_class()
    return form_class(**self.get_form_kwargs())

def get_form_class(self):
    """
    Returns the form class to use in this view
    """
    return self.form_class

def get_form_kwargs(self):
    """
    Returns the keyword arguments for instantiating the form.
    """
    kwargs = {
        'initial': self.get_initial(),
        'prefix': self.get_prefix(),
    }
    if self.request.method in ('POST', 'PUT'):
        kwargs.update({
            'data': self.request.POST,
            'files': self.request.FILES,
        })
    return kwargs

def get_initial(self):
    """
    Returns the initial data to use for forms on this view.
    """
    return self.initial.copy()

def get_prefix(self):
    """
    Returns the prefix to use for forms on this view
    """
    return self.prefix

def get_success_url(self):
    """
    Returns the supplied success URL.
    """
    if self.success_url:
        # Forcing possible reverse_lazy evaluation
        url = force_text(self.success_url)
    else:
        raise ImproperlyConfigured(
            "No URL to redirect to. Provide a success_url.")
    return url