[Bug] [Python 3.10] Crash when using postponed evaluation of annotations

[odelalleau]

🐛 Bug

Structured configs seem not to work with the upcoming postponed evaluation of annotations (https://www.python.org/dev/peps/pep-0563/) which will be the default in Python 3.10.

Obviously not really a problem yet but flagging it now as a FYI.

To reproduce

** Minimal Code/Config snippet to reproduce **

from __future__ import annotations

from dataclasses import dataclass
from omegaconf import OmegaConf

@dataclass
class Config:
    a: int = 0

cfg = OmegaConf.structured(Config)

** Stack trace/error message **

Traceback (most recent call last):
  File "test2.py", line 10, in <module>
    cfg = OmegaConf.structured(Config)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/omegaconf.py", line 134, in structured
    return OmegaConf.create(obj, parent)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/omegaconf.py", line 171, in create
    return OmegaConf._create_impl(obj=obj, parent=parent)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/omegaconf.py", line 220, in _create_impl
    element_type=element_type,
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/dictconfig.py", line 74, in __init__
    self._set_value(content)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/dictconfig.py", line 546, in _set_value
    data = get_structured_config_data(value)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/_utils.py", line 258, in get_structured_config_data
    return get_dataclass_data(obj)
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/_utils.py", line 202, in get_dataclass_data
    ref_type=type_, is_optional=is_optional, key=name, value=value, parent=None,
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/omegaconf.py", line 681, in _maybe_wrap
    key=key,
  File "/private/home/odelalleau/.conda/envs/py37-hydra/lib/python3.7/site-packages/omegaconf/omegaconf.py", line 641, in _node_wrap
    elif issubclass(type_, Enum):
TypeError: issubclass() arg 1 must be a class

[omry]

What is this supposed to do?

[omry]

Okay, I saw the answer in the pep. Thanks for the heads up.

[seminumber]

I came here to report the same bug. This is truly a bug that I encountered (using other third party tools hydra-core) and took me a whole day to figure out what is being wrong, largely because the TypeError output message is very hard to decipher. Please also consider making early assertions so that the type error reads more sensible (like type annotation for field xx is missing..)

[omry]

Are you using Python 3.10?
This issue is specific to it. Since it's not officially supported or even easily available yet I am surprised you ran into it.

[omry]

If you are not using Python 3.10 (as I suspect is the case), please file a different issue with a minimal repro.

[tmke8]

If from __future__ import annotations is used (as in the code snippet at the top), then this also happens in Python 3.7+. I just reproduced it with Python 3.7.7.

The solution should be simple: instead of using field.type, use typing.get_type_hints(cls) and then map the resolved types to the field.

[omry]

At this point this is low priority, but feel free to send a pull request.

[gibiansky]

I just hit this issue, please merge this PR ASAP! In my experience almost all code that uses types heavily uses from __future__ import annotations, so this is fairly serious.

[omry]

@gibiansky, mind jumping into the chat to tell me more about your use case?
This issue has not been a priority and the is currently no plan to fix it in 2.0 (and 2.1 is still months away).

[gibiansky]

A relatively clean workaround is to put your config types / dataclasses in a separate file in which you don't use from __future__ import annotations , then import those, since the future import is per-file.

[bo5o]

I am hitting the same issue with omegaconf 2.0.6 on Python 3.7.9. Will this go into a patch release on 2.0.x or will it be released as part of 2.1?

[omry]

It is planned to be released with 2.1.
If you don't mind trying a dev release, you can use 2.1.0dev* (e.g 2.1.10dev17). Be sure to report any issues if you do.

Note that there are some known breaking changes, you can look at the news directory for *.api_change.