Summary

No file is generated when save_spectra is called and the spectra parameter is an empty list, which can be unexpected behavior. This PR addresses that by generating an empty file and logging a warning. Completes #586.

Changes

In save_spectra:

if not isinstance(spectra, list):
    spectra = [spectra]

if len(spectra) == 0:
    logger.warning("No spectra to save. File will be empty.")
    open(file, "w").close()
    return

The diff is large because I reformatted the files in the exporting module (out of habit). I can revert these changes if desired.

Testing

Ran the following code and confirmed that an empty file was created. Unit tests are passing on my machine.

import matchms
spectra = []
matchms.exporting.save_spectra(
    spectra, file="spectra.json", export_style="json"
)