I hope I fixed everything.

Oops.

Looks good to me. I'm not sure about two things that maybe @zas and @samj1912 know more about:

• All other single-file plugins are named <pluginname>.py instead of __init__.py. Since they're packaged in zip files, this shouldn't matter, I think?
• The plugin also appears to be active if it's disabled in the UI (at least I get an Album column in the main window). Was that also the case in Picard 1.x?

All other single-file plugins are named .py instead of init.py. Since they're packaged in zip files, this shouldn't matter, I think?

I do not know what is the difference.

The plugin also appears to be active if it's disabled in the UI (at least I get an Album column in the main window). Was that also the case in Picard 1.x?

Yes. I just tested. I do not why it does that. It seems to be loaded, even if it is disabled. May be it is a bug?

All other single-file plugins are named .py instead of init.py. Since they're packaged in zip files, this shouldn't matter, I think?

Yes, it doesn't matter much the way we currently distribute the plugins as a ZIP. It does make a difference if you give this to users as single files. If it is named add_album_column.py the file can just be placed in the plugin directory as is. If it is called init.py creating a subdirectory is mandatory.

I personally don't have a strong opinion which naming to prefer with our current ZIP structure, both ways have benefits.

The plugin also appears to be active if it's disabled in the UI (at least I get an Album column in the main window). Was that also the case in Picard 1.x?

Yes. I just tested. I do not why it does that. It seems to be loaded, even if it is disabled. May be it is a bug?

Not a bug really, but a limitation of the plugin system. Picard's plugin system does not directly support a plugin like this. In some way this plugin just abuses the fact that plugins get executed on load to monkey patch Picard. It really is more a hack then a proper plugin.

There is some discussion about redesigning the plugin system, and one point definitely should be to allow for explicit activation / deactivation hooks for plugins. Together with properly defined interfaces for some UI manipulation that would allow more flexibility here.

In the meantime maybe the fact that this plugin is always active and cannot be deactivated should be mentioned in the description.

Can I request a screenshot of what this plugin looks like?

Of course!

It looks like this with Picard version 2.1.0 on Windows 10:

I get (running from pip installed version):

/usr/local/lib/python3.7/site-packages/picard/plugin.plugin_error:261: Failed loading zipped plugin 'add_album_column'

There is some sort of bug, where you need to go to the Picard's plugin directory and manually unzip the plugin file:

1. 
2. 
3. 
4. 
5. 
6. Once you do that, you can restart Picard's and it will be working
7. 
8. Before restart:
   
9. After restart:
   

@wisdomtooth This was supposed to be fixed with af3de8b . Strange, I will check tomorrow