[Bug]: External file format error on ImageSeries

[stephprince]

What happened?

When creating a new ImageSeries with an external file, pynwb now throws an error if format is not specified as "external", even if no format value was provided.

Would it be better for this to remain a warning (or removed entirely), since it is just informing the user that the value for format was automatically set to "external" because no format parameter was provided? Or should a user always have to add the format='external' argument when providing external data.

There is a separate check in the ImageSeries initialization if a different value for format is provided (e.g. if format='png' when external_file is present).

Steps to Reproduce

from pynwb.image import ImageSeries
image_series = ImageSeries(
            name="TestImageSeries",
            rate=1.0,
            external_file=["test.png"],
        )

Traceback

ImageSeries 'TestImageSeries': The value for 'format' has been changed to 'external'. If an external file is detected, setting a value for 'format' other than 'external' is deprecated.

Operating System

macOS

Python Executable

Conda

Python Version

3.13

Package Versions

No response

Code of Conduct

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• Have you ensured this bug was not already reported?

[rly]

I think if the format is the default None and an external file is detected, then the format should be changed to "external" and no message should be sent. If the format is something that is not [None, "external"] and an external file is detected, an error should be raised.