BUG: object of type 'Sentinel' has no len()

[DrorSh]

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of pytask.
• (optional) I have confirmed this bug exists on the main branch of pytask.

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I don't know why this happens, but when running pytask dag I get this error:

TypeError: object of type 'Sentinel' has no len()

Problem description

Expected Output

Expected to produce a DAG but results in an error.

[tobiasraabe]

Thanks for the report @DrorSh. Can you also add the pytask version and whether it worked with the previous one, and graphviz and python-graphviz version would be great. Conda or pip?

[DrorSh]

Hi Tobias, thanks for the quick reply!

I dug into it a bit more and found that the same error also occurs when running pytask build. I put together a minimal reproducible example:
https://gist.github.com/DrorSh/6dc689c569ed2d1fc4e5bdc3cda73602

Error reproduction

sh@DD3KGN34:~/projects/pytask_error2$ pixi shell

(pytask_error) sh@DD3KGN34:~/projects/pytask_error2$ pytask
──────────────────────────────────────────────────────────────────────────────── Start pytask session ─────────────────────────────────────────────────────────────────────────────────
Platform: linux -- Python 3.12.0, pytask 0.5.6, pluggy 1.6.0
Root: /home/sh/projects/pytask_error2
Configuration: /home/sh/projects/pytask_error2/pyproject.toml
Collected 1 task.

─────────────────────────────────────────────────────────────────────── Failures during resolving dependencies ────────────────────────────────────────────────────────────────────────

TypeError: object of type 'Sentinel' has no len()

On a side note, pytask is fantastic. I’ve been looking for a flexible workflow manager for a long time, and was very happy to find this. I’ve been using it for the last several months, and it has completely transformed how I organize my research pipelines. Happy to share a few improvement ideas as well if that’s useful.

Thanks again!

[DrorSh]

I (well... Claude Code...) found the root cause and submitted a fix: #723

The issue is that Click 8.3.1 uses Sentinel.UNSET as the default value for options without an explicit default parameter. When no -k or -m flags are provided, this sentinel value gets passed to Scanner.lex() which tries to call len() on it, causing the TypeError.

The fix adds explicit default=None to both the -m and -k click.Option definitions in src/_pytask/mark/__init__.py.

Tested with Python 3.14.0 and Click 8.3.1 - pytask now runs successfully!

[tobiasraabe]

@DrorSh, thank you so much for contributing a fix! I will shortly release a new version.

Also, thank you for your kind words! I am always open to suggestions and contributions. Feel free to open issues and we can discuss how we can make pytask more useful to you.