Update ipynb file with data from stdin fails

[goerz]

Trying to update a notebook with data coming from stdin fails. Steps to reproduce:

• Start with a notebook file notebook.ipynb (does not need to be paired)
• Create a notebook.md file by running jupytext --to=markdown notebook.ipynb
• Verify that jupytext --to=ipynb --output notebook.ipynb --update notebook.md works
• Run cat notebook.md | jupytext --to=ipynb --output notebook.ipynb --update, which should be equivalent.

This errors with jupytext.formats.JupytextFormatError: No format associated to extension '.'. The reason is that jupytext tries to get a file extension from the input file (stdin in this case) in check_file_version.

However, this is unnecessary, as the input data contains the following in the YAML header:

---
jupyter:
  jupytext:
    text_representation:
      extension: .md
      format_name: markdown
      format_version: '1.3'
      jupytext_version: 1.16.4
  kernelspec:
    display_name: Python 3 (ipykernel)
    language: python
    name: python3
---

Jupytext could get all the required information from this metadata (the jupytext.text_representation.extension, in particular).

Being able to update from stdin would be extremely helpful in a rewrite of jupytext.nvim that avoids the use of temporary files.

[mwouts]

Hey @goerz , sure that makes sense! Would you like to give a try at #1284 and let me know if it would work for you? Thanks

[goerz]

Yes, it works perfectly!