capture_preview() broken in v2.5.0

[Sparkofska]

Problem:
After updating to v2.5.0 my code is broken.

Minimal working example:
Fails in line 8 cap.capture_preview(ctxt).

import gphoto2 as gp

ctxt = gp.Context()
cap = gp.Camera()
cap.init(ctxt)

camera_file = cap.capture_preview(ctxt)
file_data = camera_file.get_data_and_size()

cap.exit(ctxt)

Error message:

  File "____.py", line 8, in <module>
    camera_file = cap.capture_preview(ctxt)
TypeError: in method 'Camera_capture_preview', argument 2 of type 'CameraFile *'

I am using python_3.10.12.

Background:
I was doing a ubuntu dist update, which erased my pip dependencies. Then I did pip install gphoto2 (got me v2.5.0) and my code was broken.

As written in the Changelog, there were changes in capture_preview(): "Parameter CameraFile Optional"
I verified by installing v2.4.0 that my example code worked before.

What do I need to do to get my code working again? What parameter do I have to pass to capture_preview()?

[jim-easterbrook]

This is because capture_preview now has two optional parameters - a CameraFile and a Context (or GPContext). If you need to pass a Context you also need to pass a CameraFile, which can be created with camera_file = gp.CameraFile(). In this case the CameraFile object is not returned by capture_preview.

The "pythonic" way to do this would be with named/keyword parameters. I'll investigate if I can do this with SWIG.

You don't normally need a Context - it's only used if you need callbacks during some functions.

[jim-easterbrook]

You can also use None instead of a CameraFile object. capture_preview will then behave as before, returning a new CameraFile object.

[jim-easterbrook]

The "pythonic" way to do this would be with named/keyword parameters. I'll investigate if I can do this with SWIG.

SWIG can create keyword arguments, but it's an all or nothing option. Changing all python-gphoto2 function arguments to keyword arguments would be a big change (and wouldn't allow overloaded functions that are currently used).

[Sparkofska]

Great! Thanks for the instant response!

Passing None instead of CameraFile works.

Thanks also for the hint of not needing a Context. I removed this variable entirely and it still works :)