group_files function returns only one dictionary

[BENR0]

Describe the bug
The group_files function used in the from_files class method of MultiScene returns only one dictionary and therefore the only a single Scene is loaded in the MultiScene.
Maybe this bug is specific to my files: I want to load multiple MSG Seviri slots with the seviri_l1b_nc reader (files from one month but only the 12:00 slots of each day).

To Reproduce

from satpy import Scene, MultiScene
from satpy.multiscene import timeseries
from pathlib import Path

file_dir = Path("data/msg")
files = file_dir.glob("*1200*.nc")

mscn = MultiScene.from_files(files, reader="seviri_l1b_nc")
mscn.load(["IR_108", "IR_039"])

Expected behavior
Each file should be loaded into a Scene. Specifically for the group_files function a list with multiple dictionaries, one for each file, should be returned.

Actual results
The returned list only contains one dictionary where the value is a list of all files.

Environment Info:

• Linux
• Satpy Version: 0.16.1
• PyResample Version: 1.12.3

Additional context
From a first look my guess would be that somehow the time difference threshold here https://github.com/pytroll/satpy/blob/master/satpy/readers/__init__.py#L463-L465 somehow fails.

[djhoese]

The group_files function needs at least a start_time from the filename patterns to be able to group files; it doesn't look like seviri_l1b_nc has that: https://github.com/pytroll/satpy/blob/master/satpy/etc/readers/seviri_l1b_nc.yaml.

If the pattern involves more fields that should be sorted by then they need to be configured in the reader like: https://github.com/pytroll/satpy/blob/master/satpy/etc/readers/abi_l1b.yaml#L14

[BENR0]

Fell kind of foolish that I didn't think about that, but that makes sense. I guess then that should be added to the readers yaml file. Should I do a PR for that?

[djhoese]

kind of foolish

Well it isn't heavily documented and is relatively new so I wouldn't feel too bad. A PR would be great. I didn't know enough about all the other readers when I made the feature so I didn't take the time to update every YAML file that required customization. I planned on doing it on a case by case basis like this.

"Pull requests are welcome" -Dave