[FIXED] Understanding TemplateResponseMixin class in django.views.generic.base module

Issue

Let's say we inherit TemplateView and till now we are not defining any methods. So the child class will somewhat look like this:

class ChildClass(TemplateView):
    """
    A default context mixin that passes the keyword arguments received by
    get_context_data() as the template context.
    """

    extra_context = None

    def get_context_data(self, **kwargs):
        kwargs.setdefault("view", self)
        if self.extra_context is not None:
            kwargs.update(self.extra_context)
        return kwargs


    """
    Intentionally simple parent class for all views. Only implements
    dispatch-by-method and simple sanity checking.
    """

    http_method_names = [
        "get",
        "post",
        "put",
        "patch",
        "delete",
        "head",
        "options",
        "trace",
    ]

    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)

    @classproperty
    def view_is_async(cls):
        handlers = [
            getattr(cls, method)
            for method in cls.http_method_names
            if (method != "options" and hasattr(cls, method))
        ]
        if not handlers:
            return False
        is_async = iscoroutinefunction(handlers[0])
        if not all(iscoroutinefunction(h) == is_async for h in handlers[1:]):
            raise ImproperlyConfigured(
                f"{cls.__qualname__} HTTP handlers must either be all sync or all "
                "async."
            )
        return is_async

    @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(
                    "The method name %s is not accepted as a keyword argument "
                    "to %s()." % (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)
            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

        # __name__ and __qualname__ are intentionally left unchanged as
        # view_class should be used to robustly determine the name of the view
        # instead.
        view.__doc__ = cls.__doc__
        view.__module__ = cls.__module__
        view.__annotations__ = cls.dispatch.__annotations__
        # Copy possible attributes set by decorators, e.g. @csrf_exempt, from
        # the dispatch method.
        view.__dict__.update(cls.dispatch.__dict__)

        # Mark the callback if the view class is async.
        if cls.view_is_async:
            markcoroutinefunction(view)

        return view

    def setup(self, request, *args, **kwargs):
        """Initialize attributes shared by all view methods."""
        if hasattr(self, "get") and not hasattr(self, "head"):
            self.head = self.get
        self.request = request
        self.args = args
        self.kwargs = kwargs

    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 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},
        )
        response = HttpResponseNotAllowed(self._allowed_methods())

        if self.view_is_async:

            async def func():
                return response

            return func()
        else:
            return response

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

        if self.view_is_async:

            async def func():
                return response

            return func()
        else:
            return response

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



    """A mixin that can be used to render a template."""

    template_name = None
    template_engine = None
    response_class = TemplateResponse
    content_type = None

    def render_to_response(self, context, **response_kwargs):
        """
        Return a response, using the `response_class` for this view, with a
        template rendered with the given context.

        Pass response_kwargs to the constructor of the response class.
        """
        response_kwargs.setdefault("content_type", self.content_type)
        return self.response_class(
            request=self.request,
            template=self.get_template_names(),
            context=context,
            using=self.template_engine,
            **response_kwargs,
        )

    def get_template_names(self):
        """
        Return a list of template names to be used for the request. Must return
        a list. May not be called if render_to_response() is overridden.
        """
        if self.template_name is None:
            raise ImproperlyConfigured(
                "TemplateResponseMixin requires either a definition of "
                "'template_name' or an implementation of 'get_template_names()'"
            )
        else:
            return [self.template_name]



    """
    Render a template. Pass keyword arguments from the URLconf to the context.
    """

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

So when as_view() is called it returns the view function which is then called by passing the request parameter, which in turns creates an object of child class, to call setup and dispatch thereby calling the GET method of the TemplateView class, assuming the request is GET type. Now as we haven't overriden the GET in our child class, the get method calls the render_to_response method of the TemplateResponseMixin class by passing only the context data.

In the render_to_response method, it returns an object of TemplateResponse class by calling with different arguments. One of it is :

request=self.request

Now self is the object of the child class, and in my knowledge it doesn't have any attribute as request. So how does this assignment works?

Solution

Callable function is being called when request comes by

View.as_view()(request)

from as_view source

def view(request, *args, **kwargs):
    self = cls(**initkwargs)
    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)

following calls View setup method which initializes attributes

def setup(self, request, *args, **kwargs):
    """Initialize attributes shared by all view methods."""
    if hasattr(self, 'get') and not hasattr(self, 'head'):
        self.head = self.get
    self.request = request
    self.args = args
    self.kwargs = kwargs

Answered By - iklinac