  from __future__ import unicode_literals
  from django.http import Http404
  from rest_framework import HTTP_HEADER_ENCODING, exceptions
  from rest_framework.settings import api_settings
  from rest_framework.utils.mediatypes import order_by_precedence, media_type_matches
  from rest_framework.utils.mediatypes import _MediaType
  
  
  class BaseContentNegotiation(object):
      def select_parser(self, request, parsers):
          raise NotImplementedError('.select_parser() must be implemented')
 
</s> remove from django.utils import six
 </s> add  </s> remove from django.core.exceptions import PermissionDenied
from django.http import Http404
 </s> add import inspect
import warnings
 </s> remove from rest_framework import HTTP_HEADER_ENCODING
from rest_framework import exceptions
 </s> add from rest_framework import exceptions, HTTP_HEADER_ENCODING </s> remove from django.db.models.query import QuerySet
 </s> add 
from rest_framework.utils.mediatypes import (
    _MediaType, order_by_precedence, media_type_matches
)
  from __future__ import unicode_literals
  from django.http import Http404
  from rest_framework import HTTP_HEADER_ENCODING, exceptions
  from rest_framework.settings import api_settings
from rest_framework.utils.mediatypes import (
    _MediaType, order_by_precedence, media_type_matches
)
from rest_framework.utils.mediatypes import (
    _MediaType, order_by_precedence, media_type_matches
)
  
  
  class BaseContentNegotiation(object):
      def select_parser(self, request, parsers):
          raise NotImplementedError('.select_parser() must be implemented')
keep keep keep keep replace replace keep keep keep keep keep
 Cleanup import following PEP 8 style guide 
rest_framework/negotiation.py