  
      def to_representation(self, value):
          return set([
              self.choice_strings_to_values.get(six.text_type(item), item) for item in value
          ])
  
  
  class FilePathField(ChoiceField):
      default_error_messages = {
          'invalid_choice': _('"{input}" is not a valid path choice.')
 
</s> remove         return set([
 </s> add         return { </s> remove         ])
 </s> add         } </s> remove         ])
 </s> add         } </s> remove         return set([
 </s> add         return { </s> remove     TRUE_VALUES = set(('t', 'T', 'true', 'True', 'TRUE', '1', 1, True))
    FALSE_VALUES = set(('f', 'F', 'false', 'False', 'FALSE', '0', 0, 0.0, False))
    NULL_VALUES = set(('n', 'N', 'null', 'Null', 'NULL', '', None))
 </s> add     TRUE_VALUES = {'t', 'T', 'true', 'True', 'TRUE', '1', 1, True}
    FALSE_VALUES = {'f', 'F', 'false', 'False', 'FALSE', '0', 0, 0.0, False}
    NULL_VALUES = {'n', 'N', 'null', 'Null', 'NULL', '', None}
        }
  
      def to_representation(self, value):
          return set([
              self.choice_strings_to_values.get(six.text_type(item), item) for item in value
        }
  
  
  class FilePathField(ChoiceField):
      default_error_messages = {
          'invalid_choice': _('"{input}" is not a valid path choice.')
keep keep keep keep replace keep keep keep keep keep
 Replaced all dict and set conversions from lists to dict and set literals. 
rest_framework/fields.py