  
  from django.core import validators
  from django.core.exceptions import ValidationError
  from django.conf import settings
  from django import forms
  from django.forms import widgets
  from django.utils.encoding import is_protected_type
  from django.utils.translation import ugettext_lazy as _
 
</s> remove     ManyToManyModel, Person, ReadOnlyManyToManyModel, Photo)
 </s> add     ManyToManyModel, Person, ReadOnlyManyToManyModel, Photo, SeveralChoicesModel) </s> remove         self.assertEqual(s.errors,  {'decimal_field': ['Ensure that there are no more than 4 digits in total.']}) </s> add 
from django.db.models.fields import BLANK_CHOICE_DASH
  
  from django.core import validators
  from django.core.exceptions import ValidationError
  from django.conf import settings
from django.db.models.fields import BLANK_CHOICE_DASH
  from django import forms
  from django.forms import widgets
  from django.utils.encoding import is_protected_type
  from django.utils.translation import ugettext_lazy as _
keep keep keep add keep keep keep keep
 Adding `BLANK_CHOICE_DASH` as a choice if the model's field isn't required 
rest_framework/fields.py