text: from __future__ import unicode_literals
  
  from rest_framework import serializers
  
  from .models import DocumentCheckout
  
  
  class DocumentCheckoutSerializer(serializers.ModelSerializer):
      def __init__(self, *args, **kwargs):
          # Hide this import otherwise strange circular import error occur
          from documents.serializers import DocumentSerializer
  
          super(DocumentCheckoutSerializer, self).__init__(*args, **kwargs)
          self.fields['document'] = DocumentSerializer()
  
      class Meta:
          model = DocumentCheckout
          read_only_fields = ('user_content_type', 'user_object_id')
  
  
  class NewDocumentCheckoutSerializer(serializers.Serializer):
      document = serializers.IntegerField()
      expiration_datetime = serializers.DateTimeField()
      block_new_version = serializers.BooleanField()
  