Hello app does not work

[BillShiyaoZhang]

Describe the bug The hello app does not work.

>> $ chainlit hello
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.13/bin/chainlit", line 5, in <module>
    from chainlit.cli import cli
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/__init__.py", line 18, in <module>
    from chainlit.action import Action
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/action.py", line 5, in <module>
    from chainlit.telemetry import trace_event
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/telemetry.py", line 12, in <module>
    from chainlit.config import config
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/config.py", line 538, in <module>
    config = load_config()
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/config.py", line 507, in load_config
    settings = load_settings()
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/chainlit/config.py", line 479, in load_settings
    code_settings = CodeSettings(action_callbacks={})
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/pydantic/_internal/_dataclasses.py", line 121, in __init__
    s.__pydantic_validator__.validate_python(ArgsKwargs(args, kwargs), self_instance=s)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/site-packages/pydantic/_internal/_mock_val_ser.py", line 100, in __getattr__
    raise PydanticUserError(self._error_message, code=self._code)
pydantic.errors.PydanticUserError: `CodeSettings` is not fully defined; you should define `Action`, then call `pydantic.dataclasses.rebuild_dataclass(CodeSettings)`.

For further information visit https://errors.pydantic.dev/2.10/u/class-not-fully-defined

To Reproduce Steps to reproduce the behavior:

1. pip install chainlit
2. chainlit hello
3. See error

Expected behavior The hello app successfully runs in browser

Desktop:

• OS: MacOS Sequoia v15.1.1
• Browser Safari v18.1.1
• Chip: M1

[dosubot[bot]]

I found related issues that might be helpful:

• https://github.com/chainlit/issues/1 The suggested solution is to rollback to chainlit version 1.0.401, as it works with pydantic 2.7.0.

• https://github.com/chainlit/issues/2 The issue was fixed in the 0.2.107 release. You can upgrade with pip install -U chainlit. Let us know if that fixes the issue for you.

To continue talking to Dosu, mention @dosu.

[Incospro-Jan]

Hi @BillShiyaoZhang ,

I just had the same error log on an existing Chainlit based application. It started about 3 hours ago. When pushing updates and re-deploying the application was crashing with the exact same error.

I looked at the CI/CD logs and found that the pydantic version changed from 2.10.1 to 2.10.2. After pinning the version in the requirements.txt to 2.10.1 I was able to succesfully re-deploy. pydantic==2.10.1 Maybe give that a try and let me know if the error disappears.

[BillShiyaoZhang]

@Incospro-Jan It works! Thank you!

[jackaldenryan]

Pinning pydantic to 2.10.1 worked for me as well, thank you!