fix #4198

Former-commit-id: 89f2bd8c8c

src/llamafactory/hparams/model_args.py

@@ -1,6 +1,8 @@
 from dataclasses import asdict, dataclass, field
 from typing import Any, Dict, Literal, Optional
 
+from typing_extensions import Self
+
 
 @dataclass
 class ModelArguments:
@@ -216,3 +218,13 @@ class ModelArguments:
 
     def to_dict(self) -> Dict[str, Any]:
         return asdict(self)
+
+    @classmethod
+    def copyfrom(cls, old_arg: Self, **kwargs) -> Self:
+        arg_dict = old_arg.to_dict()
+        arg_dict.update(**kwargs)
+        new_arg = cls(**arg_dict)
+        new_arg.compute_dtype = old_arg.compute_dtype
+        new_arg.device_map = old_arg.device_map
+        new_arg.model_max_length = old_arg.model_max_length
+        return new_arg