def __init__(self, names, prefix='validation'):
        """
        Args:
            names(list or str): list of names or just one name. The
                corresponding tensors have to be scalar.
            prefix(str): a prefix for logging
        """
        if not isinstance(names, list):
            self.names = [names]
        else:
            self.names = names
        self.prefix = prefix

        Args:
            names(list or str): list of names or just one name. The
                corresponding tensors have to be scalar.
            prefix(str): a prefix for logging
        
tensorpack/callbacks/inference.py