code: def get_string(self, key, default=UndefinedKey):
          
          value = self.get(key, default)
          if value is None:
              return None
  
          string_value = unicode(value)
          if isinstance(value, bool):
              string_value = string_value.lower()
          return string_value
docs: Return string representation of value found at key
  
          :param key: key to use (dot separated). E.g., a.b.c
          :type key: basestring
          :param default: default value if key not found
          :type default: basestring
          :return: string value
          :type return: basestring