[online-dpo] allow parse-args as list of floats

[kashif]

What does this PR do?

fixes #2106

[HuggingFaceDocBuilderDev]

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[qgallouedec]

What about this instead?

from transformers import HfArgumentParser, TrainingArguments
from dataclasses import dataclass, field
from typing import List

@dataclass
class MyArgs(TrainingArguments):
    beta: List[float] = field(default_factory=lambda: [0.1])

    def __post_init__(self):
        super().__post_init__()
        if len(self.beta) == 1:
            self.beta = self.beta[0]

parser = HfArgumentParser(MyArgs)
args = parser.parse_args_into_dataclasses()[0]
print(args.beta)

$ python 2106.py --output_dir tmp --beta 0.2
0.2
$ python 2106.py --output_dir tmp --beta 0.1 0.2
[0.1, 0.2]
$ python 2106.py --output_dir tmp
0.1

[kashif]

ah yes good idea! fixing

[qgallouedec]

To allow using args without the parser, we should check if the object has is sizeable as well:

from transformers import TrainingArguments
from dataclasses import dataclass, field

from typing import List


@dataclass
class MyArgs(TrainingArguments):
    beta: List[float] = field(default_factory=lambda: [0.1])

    def __post_init__(self):
        super().__post_init__()
        if hasattr(self.beta, "__len__") and len(self.beta) == 1:
            self.beta = self.beta[0]


args = MyArgs(output_dir="tmp", beta=0.2)
print(args.beta) # 0.2
args = MyArgs(output_dir="tmp", beta=[0.1, 0.2])
print(args.beta) # [0.1, 0.2]

[qgallouedec]

I'll just add a few tests

[qgallouedec]

LGTM thanks, just make sure to update the title