  import re
  
  from django import http
  from django.conf import settings
  from django.core.exceptions import PermissionDenied
  from django.core.mail import mail_managers
 
</s> remove from django.utils.deprecation import MiddlewareMixin
 </s> add from django.utils.deprecation import MiddlewareMixin, RemovedInDjango21Warning </s> remove from django.utils.cache import get_conditional_response
 </s> add from django.utils.cache import (
    cc_delim_re, get_conditional_response, set_response_etag,
) </s> remove           appropriately.
 </s> add           appropriately. USE_ETAGS is deprecated in favor of
          ConditionalGetMiddleware.
import warnings
  import re
import warnings
  
  from django import http
  from django.conf import settings
  from django.core.exceptions import PermissionDenied
  from django.core.mail import mail_managers
add keep keep keep keep keep
 Fixed #26447 -- Deprecated settings.USE_ETAGS in favor of ConditionalGetMiddleware. 
django/middleware/common.py