old_contents: # -*- coding: utf-8 -*-
  ''' Default configuration for the application
  
  This data must be supplemented with custom configuration to which
  URL_SHORTENER_CONFIGURATION environment variable points, overriding
  some of the values specified here.
  
  :var SQLALCHEMY_DATABASE_URI: uri of database to be used by the application.
  
  The default value serves only as documentation, and it was taken from:
  http://docs.sqlalchemy.org/en/latest/core/engines.html#database-urls
  
  :var MIN_NEW_ALIAS_LENGTH: a minimum number of characters in a newly
  generated alias
  :var MAX_NEW_ALIAS_LENGTH: a maximum number of characters in a newly
  generated alias
  :var SECRET_KEY: a secret key to be used by the application
  :var LOG_FILE: a name of file to which the application writes logs.
  :var REGISTRATION_RETRY_LIMIT: a maximum number of retries for
  registering a new shortened url
  :var GOOGLE_SAFE_BROWSING_API_KEY: a value necessary for querying
  Google Safe Browsing API.
  :var HOST_BLACKLIST_FILE: a name of file storing blacklisted hosts
  (hostnames and ip addresses). Each line must contain one host.
  '''
  SQLALCHEMY_DATABASE_URI = (
      'dialect+driver://username:password@host:port/database'
  )
  MIN_NEW_ALIAS_LENGTH = 1
  MAX_NEW_ALIAS_LENGTH = 4
  SECRET_KEY = 'a secret key'
  LOG_FILE = None
  REGISTRATION_RETRY_LIMIT = 10
  GOOGLE_SAFE_BROWSING_API_KEY = 'a key'
  HOST_BLACKLIST_FILE = 'host_blacklist.txt'
  
new_contents: # -*- coding: utf-8 -*-
  ''' Default configuration for the application
  
  This data must be supplemented with custom configuration to which
  URL_SHORTENER_CONFIGURATION environment variable points, overriding
  some of the values specified here.
  
  :var SQLALCHEMY_DATABASE_URI: uri of database to be used by the application.
  
  The default value serves only as documentation, and it was taken from:
  http://docs.sqlalchemy.org/en/latest/core/engines.html#database-urls
  
  :var MIN_NEW_ALIAS_LENGTH: a minimum number of characters in a newly
  generated alias
  :var MAX_NEW_ALIAS_LENGTH: a maximum number of characters in a newly
  generated alias
  :var SECRET_KEY: a secret key to be used by the application
  :var LOG_FILE: a name of file to which the application writes logs.
  :var REGISTRATION_RETRY_LIMIT: a maximum number of retries for
  registering a new shortened url
  :var GOOGLE_SAFE_BROWSING_API_KEY: a value necessary for querying
  Google Safe Browsing API.
  :var HOST_BLACKLIST_FILE: a name of file storing blacklisted hosts
  (hostnames and ip addresses). Each line must contain one host.
  '''
  SQLALCHEMY_DATABASE_URI = (
      'dialect+driver://username:password@host:port/database'
  )
  MIN_NEW_ALIAS_LENGTH = 1
  MAX_NEW_ALIAS_LENGTH = 4
  SECRET_KEY = 'a secret key'
  LOG_FILE = None
  REGISTRATION_RETRY_LIMIT = 10
  GOOGLE_SAFE_BROWSING_API_KEY = 'a key'
  HOST_BLACKLIST_FILE = None
  
subject: Change value of default_config.HOST_BLACKLIST_FILE