docs: def log_before(attr, level=logging.DEBUG):
      '''Decorator to log attribute's value(s) before function call.
  
      Implementation allows usage only for methods belonging to class. The class
      instance needs to have a :attr:`logger` that is derived from
      :py:class:`~creamas.logging.ObjectLogger`.
  
      :param int level: logging level
      :param str attr: name of the class instance's parameter to be logged
      '''
      def deco(func):
          @wraps(func)
          def wrapper(*args, **kwargs):
              logger = getattr(args[0], 'logger', None)
              if logger is not None:
                  logger.log_attr(level, attr)
              return func(*args, **kwargs)
          return wrapper
      return deco