old_contents: class ConfigVars(object):
      """Configuration environment variables"""
  
      # behavior
      VERBOSE = 'VERBOSE'
  
      # Mercury API URL
      MIGRATOR_API_ENDPOINT = 'MIGRATOR_API_ENDPOINT'
      # TODO some of these probably just belong in this file in another Class
      # instead of being defined in a config file (like 'mercury_id')
      ENTITY_FIELD_NAME = 'ENTITY_FIELD_NAME'
      LISTED_SERVICE_NAMES = 'LISTED_SERVICE_NAMES'
      INTERNAL_IDENTITY_URL = 'INTERNAL_IDENTITY_URL'
      INTERNAL_IDENTITY_USERNAME = 'INTERNAL_IDENTITY_USERNAME'
      INTERNAL_IDENTITY_PASSWORD = 'INTERNAL_IDENTITY_PASSWORD'
      DOMAIN = 'DOMAIN'
      DOMAIN_NAME = 'DOMAIN_NAME'
  
  class Sources(object):
      """Sources to get the configuration variables from"""
  
      ENVIRON = 'environ'
  
new_contents: class ConfigVars(object):
      """Configuration environment variables"""
  
      # behavior
      VERBOSE = 'VERBOSE'
  
      # Mercury API URL
      MERCURY_API_ENDPOINT = 'MERCURY_API_ENDPOINT'
      # TODO some of these probably just belong in this file in another Class
      # instead of being defined in a config file (like 'mercury_id')
      ENTITY_FIELD_NAME = 'ENTITY_FIELD_NAME'
      LISTED_SERVICE_NAMES = 'LISTED_SERVICE_NAMES'
      INTERNAL_IDENTITY_URL = 'INTERNAL_IDENTITY_URL'
      INTERNAL_IDENTITY_USERNAME = 'INTERNAL_IDENTITY_USERNAME'
      INTERNAL_IDENTITY_PASSWORD = 'INTERNAL_IDENTITY_PASSWORD'
      DOMAIN = 'DOMAIN'
      DOMAIN_NAME = 'DOMAIN_NAME'
  
  class Sources(object):
      """Sources to get the configuration variables from"""
  
      ENVIRON = 'environ'
  
subject: Use mercury endpoint for const config var