Passing pre_save_hook as importstring

[dleen]

Description

Passing a pre_save_hook as an importstring e.g.

--FileContentsManager.pre_save_hook='mymodule.foo_function`

fails with the following error when launching the Jupyter server:

Troubleshoot Output

    @validate("pre_save_hook")
    def _validate_pre_save_hook(self, proposal):
        value = proposal["value"]
        if isinstance(value, str):
            value = import_item(self.pre_save_hook)
        if not callable(value):
            raise TraitError("pre_save_hook must be callable")
        if self.pre_save_hook is not None:
            warnings.warn(
>               f"Overriding existing pre_save_hook ({self.pre_save_hook.__name__}) with a new one ({value.__name__}).",
                stacklevel=2,
            )
E           AttributeError: 'str' object has no attribute '__name__'

If you edit jupyter_server_config.py to import the function, then setting the value is fine.

Reproduce

Pass pre_save_hook or post_save_hook as a importstring.

Expected behavior

Passing as a string or function works equally well.

Discussion

The problem seems to be because the code assumes that self.pre_save_hook is always a function and has the __name__ dunder.

[welcome]

Thank you for opening your first issue in this project! Engagement like this is essential for open source projects! 🤗

If you haven't done so already, check out Jupyter's Code of Conduct. Also, please try to follow the issue template as it helps other other community members to contribute more effectively.

You can meet the other Jovyans by joining our Discourse forum. There is also an intro thread there where you can stop by and say Hi! 👋

Welcome to the Jupyter community! 🎉

[davidbrochart]

Thanks for opening an issue @dleen, I commented on the PR.