text: import os
  
  # retrieve the crawler's configuration options
  config = {
      "consumer_key": os.environ['TWITTER_CONSUMER_KEY'],
      "consumer_secret": os.environ['TWITTER_CONSUMER_SECRET'],
      "access_token": os.environ['TWITTER_ACCESS_TOKEN'],
      "access_token_secret": os.environ['TWITTER_ACCESS_TOKEN_SECRET'],
      "proxy_server": os.environ.get('CRAWLER_PROXY_IP')
  }
  
  # raise exception if any of the API keys above are not defined
  for key in config:
      if config[key] == '':
          if key in {'consumer_key', 'consumer_secret',
                     'access_token', 'access_token_secret'}:
              
              raise RuntimeError('Key', '"{}"'.format(key), 'has not been set')
  