draccus.dump can fail with 'TypeError: cannot create weak reference to str object'

[dlwh]

Summary

draccus.dump(...) can fail with:

TypeError: cannot create weak reference to 'str' object

We hit this while logging a dataclass config artifact from Levanter/Marin. The error is nonfatal in our caller, but it prevents config YAML artifact emission.

Context

Caller path:

with open(path, "w", encoding="utf-8") as f:
    draccus.dump(hparams, f, encoding="utf-8")

The surrounding caller is a tracker/logging utility that checks dataclasses.is_dataclass(hparams) before calling draccus.dump(...).

Observed traceback

TypeError: cannot create weak reference to 'str' object

The traceback originates from inside draccus.dump(...) when dumping our experiment config dataclass.

Notes

• This showed up repeatedly in long-running training jobs.
• In our case the training run continues, but config artifact logging is skipped.
• I do not yet have a smaller standalone repro than “nested experiment config dataclass with string fields”, but I wanted to file the bug with the exact failure mode because it is recurring.

Expected behavior

draccus.dump(...) should successfully serialize the dataclass, or fail with a more direct validation error if the input type is unsupported.

[dlwh]

🤖 I isolated a much smaller standalone repro.

This fails for me on draccus==0.8.0:

from __future__ import annotations
from dataclasses import dataclass
import io

import draccus


@dataclass
class Simple:
    cpu: float = 1.0
    name: str = "x"


buf = io.StringIO()
draccus.dump(Simple(), buf)

Observed traceback:

TypeError: cannot create weak reference to 'str' object

Relevant detail:

print(Simple.__annotations__)
# {'cpu': 'float', 'name': 'str'}

So this looks smaller than our training config issue: draccus.dump(...) appears to break when dataclass field annotations are still stringified (for example via from __future__ import annotations) and the encoder dispatch cache tries to use the string annotation as a weakref key.

I also confirmed that a real project dataclass reproduces for the same reason:

• draccus.dump(ResourceConfig()) fails the same way in our tree.