Django 2.2: Class-Based Views

def __init__(self, **kwargs):
    """
    Constructor. Called in the URLconf; can contain helpful extra
    keyword arguments, and other things.
    """
    # Go through keyword arguments, and either save their values to our
    # instance, or raise an error.
    for key, value in kwargs.items():
        setattr(self, key, value)

def _allowed_methods(self):
    return [m.upper() for m in self.http_method_names if hasattr(self, m)]

def _get_current_day(self, date):
    """Return the start date of the current interval."""
    return date

def _get_current_month(self, date):
    """Return the start date of the previous interval."""
    return date.replace(day=1)

def _get_current_year(self, date):
    """Return the start date of the current interval."""
    return date.replace(month=1, day=1)

def _get_next_day(self, date):
    """
    Return the start date of the next interval.
    The interval is defined by start date <= item date < next start date.
    """
    return date + datetime.timedelta(days=1)

def _get_next_month(self, date):
    """
    Return the start date of the next interval.
    The interval is defined by start date <= item date < next start date.
    """
    if date.month == 12:
        try:
            return date.replace(year=date.year + 1, month=1, day=1)
        except ValueError:
            raise Http404(_("Date out of range"))
    else:
        return date.replace(month=date.month + 1, day=1)

def _get_next_year(self, date):
    """
    Return the start date of the next interval.
    The interval is defined by start date <= item date < next start date.
    """
    try:
        return date.replace(year=date.year + 1, month=1, day=1)
    except ValueError:
        raise Http404(_("Date out of range"))

def _make_date_lookup_arg(self, value):
    """
    Convert a date into a datetime when the date field is a DateTimeField.
    When time zone support is enabled, `date` is assumed to be in the
    current time zone, so that displayed items are consistent with the URL.
    """
    if self.uses_datetime_field:
        value = datetime.datetime.combine(value, datetime.time.min)
        if settings.USE_TZ:
            value = timezone.make_aware(value)
    return value

def _make_single_date_lookup(self, date):
    """
    Get the lookup kwargs for filtering on a single date.
    If the date field is a DateTimeField, we can't just filter on
    date_field=date because that doesn't take the time into account.
    """
    date_field = self.get_date_field()
    if self.uses_datetime_field:
        since = self._make_date_lookup_arg(date)
        until = self._make_date_lookup_arg(date + datetime.timedelta(days=1))
        return {
            '%s__gte' % date_field: since,
            '%s__lt' % date_field: until,
        }
    else:
        # Skip self._make_date_lookup_arg, it's a no-op in this branch.
        return {date_field: date}

@classonlymethod
def as_view(cls, **initkwargs):
    """Main entry point for a request-response process."""
    for key in initkwargs:
        if key in cls.http_method_names:
            raise TypeError("You tried to pass in the %s method name as a "
                            "keyword argument to %s(). Don't do that."
                            % (key, cls.__name__))
        if not hasattr(cls, key):
            raise TypeError("%s() received an invalid keyword %r. as_view "
                            "only accepts arguments that are already "
                            "attributes of the class." % (cls.__name__, key))
    def view(request, *args, **kwargs):
        self = cls(**initkwargs)
        if hasattr(self, 'get') and not hasattr(self, 'head'):
            self.head = self.get
        self.setup(request, *args, **kwargs)
        if not hasattr(self, 'request'):
            raise AttributeError(
                "%s instance has no 'request' attribute. Did you override "
                "setup() and forget to call super()?" % cls.__name__
            )
        return self.dispatch(request, *args, **kwargs)
    view.view_class = cls
    view.view_initkwargs = initkwargs
    # take name and docstring from class
    update_wrapper(view, cls, updated=())
    # and possible attributes set by decorators
    # like csrf_exempt from dispatch
    update_wrapper(view, cls.dispatch, assigned=())
    return view

def dispatch(self, request, *args, **kwargs):
    # Try to dispatch to the right method; if a method doesn't exist,
    # defer to the error handler. Also defer to the error handler if the
    # request method isn't on the approved list.
    if request.method.lower() in self.http_method_names:
        handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
    else:
        handler = self.http_method_not_allowed
    return handler(request, *args, **kwargs)

def get(self, request, *args, **kwargs):
    self.object = self.get_object()
    context = self.get_context_data(object=self.object)
    return self.render_to_response(context)

def get_allow_future(self):
    """
    Return `True` if the view should be allowed to display objects from
    the future.
    """
    return self.allow_future

def get_context_object_name(self, obj):
    """Get the name to use for the object."""
    if self.context_object_name:
        return self.context_object_name
    elif isinstance(obj, models.Model):
        return obj._meta.model_name
    else:
        return None

def get_date_field(self):
    """Get the name of the date field to be used to filter by."""
    if self.date_field is None:
        raise ImproperlyConfigured("%s.date_field is required." % self.__class__.__name__)
    return self.date_field

def get_day(self):
    """Return the day for which this view should display data."""
    day = self.day
    if day is None:
        try:
            day = self.kwargs['day']
        except KeyError:
            try:
                day = self.request.GET['day']
            except KeyError:
                raise Http404(_("No day specified"))
    return day

def get_day_format(self):
    """
    Get a day format string in strptime syntax to be used to parse the day
    from url variables.
    """
    return self.day_format

def get_month(self):
    """Return the month for which this view should display data."""
    month = self.month
    if month is None:
        try:
            month = self.kwargs['month']
        except KeyError:
            try:
                month = self.request.GET['month']
            except KeyError:
                raise Http404(_("No month specified"))
    return month

def get_month_format(self):
    """
    Get a month format string in strptime syntax to be used to parse the
    month from url variables.
    """
    return self.month_format

def get_next_day(self, date):
    """Get the next valid day."""
    return _get_next_prev(self, date, is_previous=False, period='day')

def get_next_month(self, date):
    """Get the next valid month."""
    return _get_next_prev(self, date, is_previous=False, period='month')

def get_next_year(self, date):
    """Get the next valid year."""
    return _get_next_prev(self, date, is_previous=False, period='year')

def get_previous_day(self, date):
    """Get the previous valid day."""
    return _get_next_prev(self, date, is_previous=True, period='day')

def get_previous_month(self, date):
    """Get the previous valid month."""
    return _get_next_prev(self, date, is_previous=True, period='month')

def get_previous_year(self, date):
    """Get the previous valid year."""
    return _get_next_prev(self, date, is_previous=True, period='year')

def get_queryset(self):
    """
    Return the `QuerySet` that will be used to look up the object.
    This method is called by the default implementation of get_object() and
    may not be called if get_object() is overridden.
    """
    if self.queryset is None:
        if self.model:
            return self.model._default_manager.all()
        else:
            raise ImproperlyConfigured(
                "%(cls)s is missing a QuerySet. Define "
                "%(cls)s.model, %(cls)s.queryset, or override "
                "%(cls)s.get_queryset()." % {
                    'cls': self.__class__.__name__
                }
            )
    return self.queryset.all()

def get_slug_field(self):
    """Get the name of a slug field to be used to look up by slug."""
    return self.slug_field

def get_year(self):
    """Return the year for which this view should display data."""
    year = self.year
    if year is None:
        try:
            year = self.kwargs['year']
        except KeyError:
            try:
                year = self.request.GET['year']
            except KeyError:
                raise Http404(_("No year specified"))
    return year

def get_year_format(self):
    """
    Get a year format string in strptime syntax to be used to parse the
    year from url variables.
    """
    return self.year_format

def http_method_not_allowed(self, request, *args, **kwargs):
    logger.warning(
        'Method Not Allowed (%s): %s', request.method, request.path,
        extra={'status_code': 405, 'request': request}
    )
    return HttpResponseNotAllowed(self._allowed_methods())

def options(self, request, *args, **kwargs):
    """Handle responding to requests for the OPTIONS HTTP verb."""
    response = HttpResponse()
    response['Allow'] = ', '.join(self._allowed_methods())
    response['Content-Length'] = '0'
    return response

def setup(self, request, *args, **kwargs):
    """Initialize attributes shared by all view methods."""
    self.request = request
    self.args = args
    self.kwargs = kwargs