old_contents: import logging
  
  from flask import Blueprint
  from apikit import jsonify, request_data
  
  from spendb.lib.helpers import get_dataset
  from spendb.views.error import api_json_errors
  
  
  log = logging.getLogger(__name__)
  blueprint = Blueprint('datasets_api3', __name__)
  
  
  @blueprint.route('/datasets/<dataset>/sources')
  @api_json_errors
  def index(dataset):
      dataset = get_dataset(dataset)
      pass
  
new_contents: import logging
  
  from flask import Blueprint
  from archivekit import Source
  from apikit import jsonify, request_data
  
  from spendb.core import data_manager
  from spendb.lib.helpers import get_dataset
  from spendb.views.error import api_json_errors
  
  
  log = logging.getLogger(__name__)
  blueprint = Blueprint('sources_api3', __name__)
  
  
  @blueprint.route('/datasets/<dataset>/sources')
  @api_json_errors
  def index(dataset):
      dataset = get_dataset(dataset)
      package = data_manager.package(dataset.name)
      sources = list(package.all(Source))
      return jsonify({
          'results': sources,
          'total': len(sources)
      })
  
subject: Return a listing.