A bug in argument parser.

[ChenDaiwei-99]

Issue:
In the original code:
e2e_rlhf.py line 68

parser.add_argument(
  "--reward-model",
  type=lambda x: x.replace("facebook/opt-", ""),
  default="350m",
  choices=("350m"),
  help="Which facebook/opt-* model to use for Reward (step 2)",
)

The choices argument is mistakenly defined as a string instead of a tuple. This causes choices to be interpreted as a sequence of characters ('3', '5', '0', 'm') rather than a single valid choice.

Solution:
To fix the issue, define choices as a tuple by adding a trailing comma:

choices=("350m",)
This ensures that choices is correctly interpreted as a tuple containing a single element, "350m".