old_contents: from rest_framework import serializers
  from openbudgets.apps.contexts import models
  
  
  class ContextBaseSerializer(serializers.HyperlinkedModelSerializer):
      """Base Context serializer, exposing our defaults for contexts."""
  
      data = serializers.WritableField()
  
      class Meta:
          model = models.Context
          fields = ['id', 'url', 'entity', 'population', 'population_male',
                    'population_female', 'ground_surface', 'students', 'schools',
                    'gini_index', 'socioeconomic_index']
  
  
  class CoefficientBaseSerializer(serializers.HyperlinkedModelSerializer):
      """Base Coefficient serializer."""
  
      class Meta:
          model = models.Coefficient
          fields = ['id', 'url', 'domain', 'inflation']
  
new_contents: from rest_framework import serializers
  from openbudgets.apps.contexts import models
  
  
  class ContextBaseSerializer(serializers.HyperlinkedModelSerializer):
      """Base Context serializer, exposing our defaults for contexts."""
  
      data = serializers.WritableField()
  
      class Meta:
          model = models.Context
          fields = ['id', 'url', 'entity', 'population', 'population_male',
                    'population_female', 'ground_surface', 'students', 'schools',
                    'gini_index', 'socioeconomic_index']
  
  
  class CoefficientBaseSerializer(serializers.HyperlinkedModelSerializer):
      """Base Coefficient serializer."""
  
      class Meta:
          model = models.Coefficient
          fields = ['id', 'url', 'domain', 'inflation', 'period_start', 'period_end']
  
subject: Add period to coefficient