  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
  
  
  class ConditionalGetMiddleware(MiddlewareMixin):
 
</s> remove from django.utils.deprecation import MiddlewareMixin
 </s> add from django.utils.deprecation import MiddlewareMixin, RemovedInDjango21Warning </s> remove     If-Modified-Since, the response is replaced by an HttpNotModified.
 </s> add     If-Modified-Since, the response is replaced by an HttpNotModified. An ETag
    header is added if needed.
from django.utils.cache import (
    cc_delim_re, get_conditional_response, set_response_etag,
)
from django.utils.cache import (
    cc_delim_re, get_conditional_response, set_response_etag,
)
  from django.utils.deprecation import MiddlewareMixin
  from django.utils.http import http_date, parse_http_date_safe
  
  
  class ConditionalGetMiddleware(MiddlewareMixin):
replace keep keep keep keep keep
 Fixed #26447 -- Deprecated settings.USE_ETAGS in favor of ConditionalGetMiddleware. 
django/middleware/http.py