Handle importstring pre/post save hooks

[dleen]

Try access the name attribute on the function form of the hook, and
if it doesn't exist then use the string as the name.

Closes #753

[welcome]

Thanks for submitting your first pull request! You are awesome! 🤗

If you haven't done so already, check out Jupyter's Code of Conduct. Also, please make sure you followed the pull request template, as this will help us review your contribution more quickly.

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

Welcome to the Jupyter community! 🎉

[codecov-commenter]

Codecov Report

Merging #754 (123d47c) into main (cd1b1b8) will decrease coverage by 0.11%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #754      +/-   ##
==========================================
- Coverage   70.68%   70.56%   -0.12%     
==========================================
  Files          62       62              
  Lines        7620     7620              
  Branches     1218     1215       -3     
==========================================
- Hits         5386     5377       -9     
- Misses       1860     1864       +4     
- Partials      374      379       +5     

Impacted Files	Coverage Δ
jupyter_server/services/contents/manager.py	83.65% <0.00%> (+1.46%)	⬆️
jupyter_server/base/zmqhandlers.py	52.91% <0.00%> (-4.24%)	⬇️
jupyter_server/services/kernels/kernelmanager.py	80.63% <0.00%> (-1.91%)	⬇️
jupyter_server/services/contents/filemanager.py	72.46% <0.00%> (-0.81%)	⬇️
jupyter_server/services/kernels/handlers.py	58.86% <0.00%> (-0.22%)	⬇️
jupyter_server/serverapp.py	65.16% <0.00%> (-0.19%)	⬇️
jupyter_server/utils.py	62.20% <0.00%> (+2.87%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cd1b1b8...123d47c. Read the comment docs.

[davidbrochart]

Thanks @dleen for opening this PR.
I think the problem here is that the hook passed on the command line with:

--FileContentsManager.pre_save_hook='mymodule.foo_function'

is being validated as a new hook, but is also treated as an already existing hook, which it isn't because otherwise it would have been validated and converted to a callable.
Because we know that a validated hook is a callable and not a string anymore, I think a better solution would be to replace this line:

        if self.pre_save_hook is not None:

with:

        if callable(self.pre_save_hook):

[dleen]

Yep that solution makes more sense!

[blink1073]

Kicking CI

[blink1073]

Thanks! The minimum version check is being handled in #756

[welcome]

Congrats on your first merged pull request in this project! 🎉

Thank you for contributing, we are very proud of you! ❤️