{placeholder_token} vs *s in inference 

In the fine tune code, there is an assert hard code the special token as {placeholder_tokne}. 
```assert (
            "{placeholder_token}" in args.prompt_template
        ), "You must specify the location of placeholder token by '{placeholder_token}'"
```

what is the logic we use {placeholder_token} in fine-tuning, but *s in pre-train and inference