Can't save checkpoint to file descriptor.

[GLivshits]

System Info

safetensors==0.4.5
torch==2.4.0+cu124

Information

• The official example scripts
• My own modified scripts

Reproduction

import io
import torch
from safetensors.torch import save_file as safetensors_save

data = {}
tensor_shape = (64, 128, 256)
num_tensors = 16
for i in range(num_tensors):
    data[str(i)] = torch.randn(*tensor_shape)

stream = io.BytesIO()
out = safetensors_save(data, stream)

Error:

TypeError: argument 'filename': expected str, bytes or os.PathLike object, not BytesIO

Expected behavior

I've expected serialized checkpoint bytes to be written to buffer.
It would be convenient to do so for:

1. Further uploading from file object.
2. Use custom file object, representing database file.

There are only options to serialize checkpoint and get bytes (which is not convenient when checkpoint is large and it is materialized only on master process), and to serialize checkpoint to specified filename.