# documentación de Django - 1.10.7

# Código fuente para django.middleware.http

    from django.utils.cache import get_conditional_response
    from django.utils.deprecation import MiddlewareMixin
    from django.utils.http import http_date, parse_http_date_safe, unquote_etag

    class ConditionalGetMiddleware(MiddlewareMixin):
        """
        Handles conditional GET operations. If the response has an ETag or
        Last-Modified header, and the request has If-None-Match or
        If-Modified-Since, the response is replaced by an HttpNotModified.

        Also sets the Date and Content-Length response-headers.
        """
        def process_response(self, request, response):
            response['Date'] = http_date()
            if not response.streaming and not response.has_header('Content-Length'):
                response['Content-Length'] = str(len(response.content))

            etag = response.get('ETag')
            last_modified = response.get('Last-Modified')
            if last_modified:
                last_modified = parse_http_date_safe(last_modified)

            if etag or last_modified:
                return get_conditional_response(
                    request,
                    etag=unquote_etag(etag),
                    last_modified=last_modified,
                    response=response,
                )

            return response