  from django.utils import timezone
  from django.utils.functional import cached_property
  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework.compat import Mapping, postgres_fields
  from rest_framework.exceptions import ErrorDetail, ValidationError
  from rest_framework.fields import get_error_detail, set_value
  from rest_framework.settings import api_settings
  from rest_framework.utils import html, model_meta, representation
  from rest_framework.utils.field_mapping import (
 
</s> remove     Mapping, MaxLengthValidator, MaxValueValidator, MinLengthValidator,
 </s> add     MaxLengthValidator, MaxValueValidator, MinLengthValidator, </s> remove from rest_framework.compat import MutableMapping, coreapi
 </s> add from rest_framework.compat import coreapi </s> remove from rest_framework.compat import Mapping
 </s> add 
from rest_framework.compat import postgres_fields
  from django.utils import timezone
  from django.utils.functional import cached_property
  from django.utils.translation import ugettext_lazy as _
  
from rest_framework.compat import postgres_fields
  from rest_framework.exceptions import ErrorDetail, ValidationError
  from rest_framework.fields import get_error_detail, set_value
  from rest_framework.settings import api_settings
  from rest_framework.utils import html, model_meta, representation
  from rest_framework.utils.field_mapping import (
keep keep keep keep replace keep keep keep keep keep
 Remove unnecessary compatibility shims from rest_framework/compat.py (#6631)

For Python 3, collections.abc.Mapping and collections.abc.MutableMapping
are always available from the stdlib. 
rest_framework/serializers.py